Sets up a view with the frame rectangle, which is specified in the coordinate system of its eventual parent, and assigns the BView an identifying name, which can be NULL.

When it's created, a BView doesn't belong to a window and has no parent. It's assigned a parent by having another BView adopt it with the AddChild() function. If the other view is in a window, the BView becomes part of that window's view hierarchy. A BView can be made a child of the window's top view by calling BWindow's version of the AddChild() function.

When the BView gains a parent, the values in frame are interpreted in the parent's coordinate system. The sides of the view must be aligned on screen pixels. Therefore, the frame rectangle should not contain coordinates with fractional values. Fractional coordinates will be rounded to the first lower whole number (for example 1.2 will be rounded down to 1.0).

The resizingMode mask determines the behavior of the view when its parent is resized. It should combine one constant for horizontal resizing,

• B_FOLLOW_LEFT

• B_FOLLOW_RIGHT

• B_FOLLOW_LEFT_RIGHT

• B_FOLLOW_H_CENTER

with one for vertical resizing:

• B_FOLLOW_TOP

• B_FOLLOW_BOTTOM

• B_FOLLOW_TOP_BOTTOM

• B_FOLLOW_V_CENTER

For example, if B_FOLLOW_LEFT is chosen, the margin between the left side of the view and the left side of its parent will remain constant—the view will "follow" the parent's left side. Similarly, if B_FOLLOW_RIGHT is chosen, the view will follow the parent's right side. If B_FOLLOW_H_CENTER is chosen, the view will maintain a constant relationship to the horizontal center of the parent.

If the constants name opposite sides of the view rectangle—left and right, or top and bottom—the view will necessarily be resized in that dimension when the parent is. For example, B_FOLLOW_LEFT_RIGHT means that the margin between the left side of the view and left side of the parent will remain constant, as will the margin between the right side of the view and the right side of the parent. As the parent is resized horizontally, the child will be resized with it. Note that B_FOLLOW_LEFT_RIGHT is not the same as combining B_FOLLOW_LEFT and B_FOLLOW_RIGHT, an illegal move. The resizingMode mask can contain only one horizontal constant and one vertical constant.

If a side is not mentioned in the mask, the distance between that side of the view and the corresponding side of the parent is free to fluctuate. This may mean that the view will move within its parent's coordinate system when the parent is resized. B_FOLLOW_RIGHT plus B_FOLLOW_BOTTOM, for example, would keep a view from being resized, but the view will move to follow the right bottom corner of its parent whenever the parent is resized. B_FOLLOW_LEFT plus B_FOLLOW_TOP prevents a view from being resized and from being moved.

In addition to the constants listed above, there are two other possibilities:

• B_FOLLOW_ALL_SIDES

• B_FOLLOW_NONE

B_FOLLOW_ALL_SIDES is a shorthand for B_FOLLOW_LEFT_RIGHT and B_FOLLOW_TOP_BOTTOM. It means that the view will be resized in tandem with its parent, both horizontally and vertically.

B_FOLLOW_NONE behaves just like B_FOLLOW_LEFT | B_FOLLOW_TOP; the view maintains the same position in its parent's coordinate system, but not in the screen coordinate system.

Typically, a parent view is resized because the user resizes the window it's in. When the window is resized, the top view is too. Depending on how the resizingMode flag is set for the top view's children and for the descendants of its children, automatic resizing can cascade down the view hierarchy. A view can also be resized programmatically by the ResizeTo() and ResizeBy() functions.

The resizing mode can be changed after construction with the SetResizingMode() function.

The flags mask determines what kinds of notifications the BView will receive. It can be any combination of the following constants:

If none of these constants apply, flags can be NULL. The flags can be reset after construction with the SetFlags() function.

See also: BHandler::SetName()

Frees all memory the BView allocated, and ensures that each of the BView's descendants in the view hierarchy is also destroyed.

It's an error to delete a BView while it remains attached to a window. Call RemoveChild() or RemoveSelf() before using the delete operator.

Implemented by derived classes to complete the initialization of the BView when it's assigned to a window. A BView is assigned to a window when it, or one of its ancestors in the view hierarchy, becomes a child of a view already attached to a window.

AttachedToWindow() is called immediately after the BView is formally made a part of the window's view hierarchy and after it has become known to the Application Server and its graphics parameters are set. The Window() function can identify which BWindow the BView belongs to.

All of the BView's children, if it has any, also become attached to the window and receive their own AttachedToWindow() notifications. Parents receive the notification before their children, but only after all views have become attached to the window and recognized as part of the window's view hierarchy. This function can therefore depend on all ancestor and descendant views being in place.

For example, AttachedToWindow() can be implemented to set a view's background color to the same color as its parent, something that can't be done before the view belongs to a window and knows who its parent is.

void MyView::AttachedToWindow()
{
   if ( Parent() )
      SetViewColor(Parent()->ViewColor());
   baseClass::AttachedToWindow();
}

The AllAttached() notification follows on the heels of AttachedToWindow(), but works its way up the view hierarchy rather than down. When AllAttached() is called for a BView, all its descendants have received both AttachedToWindow() and AllAttached() notifications. Therefore, parent views can depend on any calculations that their children make in either function. For example, a parent can resize itself to fit the size of its children, where their sizes depend on calculations done in AttachedToWindow().

The default (BView) version of both these functions are empty.

See also: AddChild()

Implemented by derived classes to make any adjustments necessary when the BView is about to be removed from a window's view hierarchy. These two functions parallel the more commonly implemented AttachedToWindow() and AllAttached() functions.

DetachedFromWindow() notifications work their way down the hierarchy of views being detached, followed by AllDetached() notifications, which work their way up the hierarchy. The second function call permits an ancestor view to take actions that depend on calculations a descendant might have to make when it's first notified of being detached.

The BView is still attached to the window when both functions are called.

Implemented by derived classes to draw the updateRect portion of the view. The update rectangle is stated in the BView's coordinate system.

Draw() is called as the result of update messages whenever the view needs to present itself on-screen. This may happen when:

• The window the view is in is first shown on-screen, or shown after being hidden (see the BWindow version of the Hide() function).

• The view is made visible after being hidden (see BView's Hide() function).

• Obscured parts of the view are revealed, as when a window is moved from in front of the view or an image is dragged across it.

• The view is resized.

• The contents of the view are scrolled (see ScrollBy()).

• A child view is added, removed, or resized.

• A rectangle has been invalidated that includes at least some of the view (see Invalidate()).

• CopyBits() can't completely fill a destination rectangle within the view.

Draw() is also called from a BPrintJob object's DrawView() function to draw the view on a printed page. IsPrinting() returns true when the BView is drawing for the printer and false when it's drawing to the screen. When printing, you may want to recalculate layouts, substitute fonts, turn antialiasing off, scale the size of a coordinate unit, or make other adjustments to ensure the quality of the printed image.

When drawing to the screen, the updateRect is the smallest rectangle that encloses the current clipping region for the view. Since the Application Server won't render anything on-screen that's outside the clipping region, an application will be more efficient if it avoids producing drawing instructions for images that don't intersect with the rectangle. For still more efficiency and precision, you can ask for the clipping region itself (by calling GetClippingRegion()) and confine drawing to images that intersect with it.

When printing, the updateRect matches the rectangle passed to DrawView() and may lie outside the clipping region. The clipping region is not enforced for printing, but the Print Server clips the BView's drawing to the specified rectangle.

See also: BWindow::UpdateIfNeeded()

This function is similar (in fact, almost identical) to Draw(). The only difference is that DrawAfterChildren() is called after all children have drawn during a screen update. This is in contrast to Draw(), which draws before any children have drawn. In general, Draw() will be used for almost all of your drawing needs; DrawAfterChildren() is intended for use in the rare circumstances where you wish a view to be able to draw on top of its child views.

Other details are as for Draw().

Implemented by derived classes to respond to a notification that the view has moved within its parent's coordinate system. newLocation gives the new location, within the coordinate system of the view's window, of the left top corner of the BView's frame rectangle.

FrameMoved() is called only if the B_FRAME_EVENTS flag is set and the BView is attached to a window.

If the view is both moved and resized, FrameMoved() is called before FrameResized(). This might happen, for example, if the BView's automatic resizing mode is a combination of B_FOLLOW_TOP_BOTTOM and B_FOLLOW_RIGHT and its parent is resized both horizontally and vertically.

BView's version of this function is empty.

Currently, FrameMoved() is also called when a hidden window is shown on-screen.

See also: MoveBy(), BWindow::FrameMoved(), SetFlags()

Implemented by derived classes to respond to a notification that the view has been resized. The arguments state the new width and height of the view. The resizing could have been the result of a user action (resizing the window) or of a programmatic one (calling ResizeTo() or ResizeBy()).

FrameResized() is called only if the B_FRAME_EVENTS flag is set and the BView is attached to a window.

BView's version of this function is empty.

See also: BWindow::FrameResized(), SetFlags()

GetPreferredSize() is implemented by derived classes to write the preferred width and height of the view into the variables the width and height arguments refer to. Derived classes generally make this calculation based on the view's contents. For example, a BButton object reports the optimal size for displaying the button border and label given the current font.

ResizeToPreferred() resizes the BView's frame rectangle to the preferred size, keeping its left and top sides constant.

See also: ResizeTo()

Implemented by derived classes to respond to a B_KEY_DOWN message reporting keyboard input. Whenever a BView is the focus view of the active window, it receives a KeyDown() notification for each character the user types, except for those that:

• Are produced while a Command key is held down. Command key events are interpreted as keyboard shortcuts.

• Are produced by the Tab key when an Option key is held down. Option+Tab events are invariably interpreted as instructions to change the focus view (for keyboard navigation); they work even where Tab alone does not.

• Can operate the default button in a window. The BButton object's KeyDown() function is called, rather than the focus view's.

The first argument, bytes, is an array that encodes the character mapped to the key the user pressed. The second argument, numBytes, tells how many bytes are in the array; there will always be at least one. The bytes value follows the character encoding of the BView's font. Typically, the encoding is Unicode UTF-8 (B_UNICODE_UTF8), so there may be more than one byte per character. The bytes array is not null-terminated; '0' is a valid character value.

The character value takes into account any modifier keys that were held down or keyboard locks that were on at the time of the keystroke. For example, Shift+i is reported as uppercase 'I' (0x49) and Control+i is reported as a B_TAB (0x09).

Single-byte characters can be tested against ASCII codes and these constants:

• B_BACKSPACE

• B_ENTER

• B_RETURN

• B_SPACE

• B_TAB

• B_ESCAPE

• B_LEFT_ARROW

• B_RIGHT_ARROW

• B_UP_ARROW

• B_DOWN_ARROW

• B_INSERT

• B_DELETE

• B_HOME

• B_END

• B_PAGE_UP

• B_PAGE_DOWN

• B_FUNCTION_KEY

B_ENTER and B_RETURN are the same character, a newline ('\n').

Only keys that generate characters produce key-down events; the modifier keys on their own do not.

You can determine which modifier keys were being held down at the time of the event by calling BLooper's CurrentMessage() function and looking up the "modifiers" entry in the BMessage it returns. If the bytes character is B_FUNCTION_KEY and you want to know which key produced the character, you can look up the "key" entry in the BMessage and test it against these constants:

• B_F1_KEY

• B_F1_KEY

• B_F2_KEY

• B_F3_KEY

• B_F4_KEY

• B_F5_KEY

• B_F6_KEY

• B_F7_KEY

• B_F8_KEY

• B_F9_KEY

• B_F10_KEY

• B_F11_KEY

• B_F12_KEY

• B_PRINT_KEY (Print Screen)

• B_SCROLL_KEY (Scroll Lock)

• B_PAUSE_KEY

For example:

if ( bytes[0] == B_FUNCTION_KEY ) {
   BMessage *msg = Window()->CurrentMessage();
   if ( msg ) {
      int32 key;
      msg->FindInt32("key", &key);
      switch ( key ) {
      case B_F1_KEY:
         . . .
         break;
      case B_F2_KEY:
         . . .
         break;
      . . .
      }
   }
}

The BView version of KeyDown() handles keyboard navigation from view to view through B_TAB characters. If the view you define is navigable, its KeyDown() function should permit B_SPACE characters to operate the object and perhaps allow the arrow keys to navigate inside the view. It should also call the inherited version of KeyDown() to enable between-view navigation. For example:

void MyView::KeyDown(const char *bytes, int32 numBytes)
{
   if ( numBytes == 1 ) {
      switch ( bytes[0] ) {
      case B_SPACE:
         /* mimic a click in the view*/
         break;
      case B_RIGHT_ARROW:
         /* move one position to the right in the view*/
         break;
      case B_LEFT_ARROW:
         /* move one position to the left in the view*/
         break;
      default:
         baseClass::KeyDown(bytes, numBytes);
         break;
      }
   }
}

If your BView is navigable but needs to respond to B_TAB characters—for example, if it permits users to insert tabs in a text string—its KeyDown() function should simply grab the characters and not pass them to the inherited function. Users will have to rely on the Option+Tab combination to navigate from your view.

See also: the Keyboard Information special topic, B_KEY_DOWN in the Keyboard Messages appendix, BWindow::SetDefaultButton(), modifiers()

Implemented by derived classes to respond to a B_KEY_UP message reporting that the user released a key on the keyboard. The same set of keys that produce B_KEY_DOWN messages when they're pressed produce B_KEY_UP messages when they're released. The bytes and numBytes arguments encode the character mapped to the key the user released; they work exactly like the same arguments passed to KeyDown().

Some B_KEY_DOWN messages are swallowed by the system and are never dispatched by calling KeyDown(); others are dispatched, but not to the focus view. In contrast, all B_KEY_UP messages are dispatched by calling KeyUp() for the focus view of the active window. Since the focus view and active window can change between the time a key is pressed and the time it's released, this may or may not be the same BView that was notified of the B_KEY_DOWN message.

Augments the BHandler version of MessageReceived() to handle scripting messages for the BView.

MouseDown() is a hook function that's invoked when the user depresses a mouse button (or other pointing device button, not including joysticks). The location of the cursor at the time of the event is given by point in the BView's coordinates. See B_MOUSE_DOWN for the message format. Also see SetMouseEventMask() for information on extending the view's event mask while the mouse is being held down.

The BView version of MouseDown() is empty.

Implemented by derived classes to respond to reports of mouse-moved events associated with the view. As the user moves the cursor over a window, the Application Server generates a continuous stream of messages reporting where the cursor is located.

The first argument, point, gives the cursor's new location in the BView's coordinate system. The second argument, transit, is one of four constants,

• B_ENTERED_VIEW

• B_INSIDE_VIEW

• B_EXITED_VIEW

• B_OUTSIDE_VIEW

which explains whether the cursor has just entered the visible region of the view, is now inside the visible region having previously entered, has just exited from the view, or is currently outside the visible region of the view. When the cursor passes from one view to another, MouseMoved() is called on each of the BViews, once with a transit code of B_EXITED_VIEW and the other with a code of B_ENTERED_VIEW.

If the user is dragging a bundle of information from one location to another, the final argument, message, is a pointer to the BMessage object that holds the information. If a message isn't being dragged, message is NULL.

The default version of MouseMoved() is empty.

Implemented by derived classes to respond to a message reporting a mouse-up event within the view. The location of the cursor at the time of the event is given by point in the BView's coordinates.

Implemented by derived classes to do something at regular intervals. Pulses are regularly timed events, like the tick of a clock or the beat of a steady pulse. A BView receives Pulse() notifications when no other messages are pending, but only if it asks for them with the B_PULSE_NEEDED flag.

The interval between Pulse() calls can be set with BWindow's SetPulseRate() function. The default interval is around 500 milliseconds. The pulse rate is the same for all views within a window, but can vary between windows.

Derived classes can implement a Pulse() function to do something that must be repeated continuously. However, for time-critical actions, you should implement your own timing mechanism.

The BView version of this function is empty.

See also: SetFlags() the BView constructor,

Implemented by derived classes to respond to a notification that the BView has become the target of the scroller BScrollView object. This function is called when the BScrollView sets its target, which it does on construction. The target is the object whose contents will be scrolled.

BView's implementation of this function is empty.

See also: The various scrolling-related functions in BView Input Related Functions.

Implemented by derived classes to take whatever steps are necessary when the BView's window becomes the active window, or when the window gives up that status. If active is true, the window has become active. If active is false, it no longer is the active window.

All objects in the view hierarchy receive WindowActivated() notifications when the status of the window changes.

BView's version of this function is empty.

See also: BWindow::WindowActivated()

Archives the BView in the BMessage archive.

See also: BArchivable::Archive(), Instantiate() static function

Returns the BView's bounds rectangle.

These functions convert points and rectangles to and from the coordinate system of the BView's parent. ConvertToParent() converts localPoint or localRect from the BView's coordinate system to the coordinate system of its parent BView. ConvertFromParent() does the opposite; it converts parentPoint or parentRect from the coordinate system of the BView's parent to the BView's own coordinate system.

If the point or rectangle is passed by value, the function returns the converted value. If a pointer is passed, the conversion is done in place.

Both functions fail if the BView isn't attached to a window.

See also: ConvertToScreen()

ConvertToScreen() converts localPoint or localRect from the BView's coordinate system to the global screen coordinate system. ConvertFromScreen() makes the opposite conversion; it converts screenPoint or screenRect from the screen coordinate system to the BView's local coordinate system.

If the point or rectangle is passed by value, the function returns the converted value. If a pointer is passed, the conversion is done in place.

The screen coordinate system has its origin, (0.0, 0.0), at the left top corner of the main screen.

Neither function will work if the BView isn't attached to a window.

See also: BWindow::ConvertToScreen(), ConvertToParent()

Returns the BView's frame rectangle. The frame rectangle is first set by the BView constructor and is altered only when the view is moved or resized. It's stated in the coordinate system of the BView's parent.

These functions hide a view and show it again.

Hide() makes the view invisible without removing it from the view hierarchy. The visible region of the view will be empty and the BView won't receive update messages. If the BView has children, they also are hidden.

Show() unhides a view that had been hidden. This function doesn't guarantee that the view will be visible to the user; it merely undoes the effects of Hide(). If the view didn't have any visible area before being hidden, it won't have any after being shown again (given the same conditions).

Calls to Hide() and Show() can be nested. For a hidden view to become visible again, the number of Hide() calls must be matched by an equal number of Show() calls.

However, Show() can only undo a previous Hide() call on the same view. If the view became hidden when Hide() was called to hide the window it's in or to hide one of its ancestors in the view hierarchy, calling Show() on the view will have no effect. For a view to come out of hiding, its window and all its ancestor views must be unhidden.

Hide() and Show() can affect a view before it's attached to a window. The view will reflect its proper state (hidden or not) when it becomes attached. Views are created in an unhidden state.

See also: BWindow::Hide(), IsHidden()

Returns true if the BView is the current focus view for its window, and false if it's not. The focus view changes as the user chooses one view to work in and then another—for example, as the user moves from one text field to another when filling out an on-screen form. The change is made programmatically through the MakeFocus() function.

See also: BWindow::CurrentFocus()

Returns true if the view has been hidden by the Hide() function, and false otherwise.

This function returns true whether Hide() was called to hide the BView itself, to hide an ancestor view, or to hide the BView's window. When a window is hidden, all its views are hidden with it. When a BView is hidden, all its descendants are hidden with it.

If the view has no visible region—perhaps because it lies outside its parent's frame rectangle or is obscured by a window in front—this function may nevertheless return false. It reports only whether the Hide() function has been called to hide the view, hide one of the view's ancestors in the view hierarchy, or hide the window where the view is located.

If the BView isn't attached to a window, IsHidden() returns the state that it will assume when it becomes attached. By default, views are not hidden.

Returns true if the BView is being asked to draw for the printer, and false if the drawing it produces will be rendered on-screen (or if the BView isn't being asked to draw at all).

This function's result is only reliable when called from within Draw() or DrawAfterChildren() to determine whether the drawing it does is destined for the printer or the screen. When drawing to the printer, the BView may choose different parameters—such as fonts, bitmap images, or colors—than when drawing to the screen.

Note

You should avoid calling this function from outside Draw() and DrawAfterChildren(); however, if you absolutely have to do it, lock the view first. Failure to do so may bring up the debugger—if not in BeOS 5, it may in future versions of BeOS.

See also: the BPrintJob class

Returns the coordinates of the left top corner of the view—the smallest x and y coordinate values within the bounds rectangle.

See also: BRect::LeftTop(), Bounds()

These functions move the view in its parent's coordinate system without altering its size.

MoveBy() adds horizontal coordinate units to the left and right components of the frame rectangle and vertical units to the top and bottom components. If horizontal and vertical are positive, the view moves downward and to the right. If they're negative, it moves upward and to the left.

MoveTo() moves the upper left corner of the view to point or to (x, y) in the parent view's coordinate system and adjusts all coordinates in the frame rectangle accordingly.

Neither function alters the BView's bounds rectangle or coordinate system.

None of the values passed to these functions should specify fractional coordinates; the sides of a view must line up on screen pixels. Fractional values will be rounded to the closest whole number.

If the BView is attached to a window, these functions cause its parent view to be updated, so the BView is immediately displayed in its new location. If it doesn't have a parent or isn't attached to a window, these functions merely alter its frame rectangle.

See also: FrameMoved(), ResizeBy(), Frame()

These functions resize the view, without moving its left and top sides. ResizeBy() adds horizontal coordinate units to the width of the view and vertical units to the height. ResizeTo() makes the view width units wide and height units high. Both functions adjust the right and bottom components of the frame rectangle accordingly.

Since a BView's frame rectangle must be aligned on screen pixels, only integral values should be passed to these functions. Values with fractional components will be rounded to the nearest whole integer.

If the BView is attached to a window, these functions cause its parent view to be updated, so the BView is immediately displayed in its new size. If it doesn't have a parent or isn't attached to a window, these functions merely alter its frame and bounds rectangles.

Note

If the view isn't attached to a window, its frame and bounds rectangles are adjusted, but its children, if any, don't get corresponding adjustments.

See also: FrameResized(), MoveBy(), Frame(), BRect::Width()

These functions set and return the flags that inform the Application Server about the kinds of notifications the BView should receive. The mask set by SetFlags() and the return value of Flags() is formed from combinations of the following constants:

• B_WILL_DRAW

• B_FULL_UPDATE_ON_RESIZE

• B_FRAME_EVENTS

• B_PULSE_NEEDED

• B_NAVIGABLE

• B_NAVIGABLE_JUMP

• B_SUBPIXEL_PRECISE

The flags are first set when the BView is constructed; they're explained in the description of the BView constructor. The mask can be 0.

To set just one of the flags, combine it with the current setting:

myView->SetFlags(Flags() | B_FRAME_EVENTS);

See also: The BView constructor, SetResizingMode()

Sets and retrieves the local origin of the BView's coordinate system.

The actual origin used by the Application Server is the sum of the local origin (as set by this method) and the origins stored on the state stack (properly scaled).

These functions set and return the BView's automatic resizing mode. The resizing mode is first set when the BView is constructed. The various possible modes are explained where the constructor is described.

See also: SetFlags()

Sets the specified cursor as the view's cursor; while the mouse is inside the view, this cursor will be displayed (unless of course the cursor is hidden or obscured).

If sync is true, the Application Server will be synchronized by this call, forcing the change to take place immediately. If sync is false, the change will take place when the Application Server naturally gets to the change in its queue of pending requests.

Returns the BWindow to which the BView belongs, or NULL if the BView isn't attached to a window. This function returns the same object that Looper() (inherited from the BHandler class) does—except that Window() returns it more specifically as a pointer to a BWindow and Looper() returns it more generally as a pointer to a BLooper.

See also: BHandler::Looper() in the Application Kit, AddChild(), BWindow::AddChild(), AttachedToWindow()

AddChild() makes aView a child of the BView, provided that aView doesn't already have a parent. The new child is added to the BView's list of children immediately before the named sibling BView. If the sibling is NULL (as it is by default), aView isn't added in front of any other view—in other words, it's added to the end of the list. If the BView is attached to a window, aView and all its descendants become attached to the same window. Each of them is notified of this change through AttachedToWindow() and AllAttached() function calls.

AddChild() fails if aView already belongs to a view hierarchy. A view can live with only one parent at a time. It also fails if sibling is not already a child of the BView.

RemoveChild() severs the link between the BView and aView, so that aView is no longer a child of the BView; aView retains all its own children and descendants, but they become an isolated fragment of a view hierarchy, unattached to a window. Each removed view is notified of this change through DetachedFromWindow() and AllDetached() function calls.

A BView must be removed from a window before it can be destroyed.

If it succeeds in removing aView, RemoveChild() returns true. If it fails, it returns false. It will fail if aView is not, in fact, a current child of the BView.

When a BView object becomes attached to a BWindow, two other connections are automatically established for it:

• The view is added to the BWindow's flat list of BHandler objects, making it an eligible target for messages the BWindow dispatches.

• The BView's parent view becomes its next handler. Messages that the BView doesn't recognize will be passed to its parent.

Removing a BView from a window's view hierarchy also removes it from the BWindow's flat list of BHandler objects; the BView will no longer be eligible to handle messages dispatched by the BWindow.

See also: BWindow::AddChild(), BLooper::AddHandler(), BHandler::SetNextHandler(), RemoveSelf(), AttachedToWindow(), DetachedFromWindow()

Returns the BView identified by name, or NULL if the view can't be found. Names are assigned by the BView constructor and can be modified by the SetName() function inherited from BHandler.

FindView() begins the search by checking whether the BView's name matches name. If not, it continues to search down the view hierarchy, among the BView's children and more distant descendants. To search the entire view hierarchy, use the BWindow version of this function.

These functions provide various ways of navigating the view hierarchy. Parent() returns the BView's parent view, unless the parent is the top view of the window, in which case it returns NULL. It also returns NULL if the BView doesn't belong to a view hierarchy and has no parent.

All the children of the same parent are arranged in a linked list. NextSibling() returns the next sibling of the BView in the list, or NULL if the BView is the last child of its parent. PreviousSibling() returns the previous sibling of the BView, or NULL if the BView is the first child of its parent.

ChildAt() returns the view at index in the list of the BView's children, or NULL if the BView has no such child. Indices begin at 0 and there are no gaps in the list. CountChildren() returns the number of children the BView has. If the BView has no children, CountChildren() returns NULL, as will ChildAt() for all indices, including 0.

To scan the list of a BView's children, you can increment the index passed to ChildAt() until it returns NULL. However, it's more efficient to ask for the first child and then use NextSibling() to walk down the sibling list. For example:

BView *child;
if ( child = myView->ChildAt(0) ) {
   while ( child ) {
      . . .
      child = child->NextSibling();
   }
}

Removes the BView from its parent and returns true, or returns false if the BView doesn't have a parent or for some reason can't be removed from the view hierarchy.

This function acts just like RemoveChild(), except that it removes the BView itself rather than one of its children.

See also: AddChild()

These functions instruct the Application Server to display a rectangular outline that will track the movement of the cursor. BeginRectTracking() puts the rectangle on-screen and initiates tracking; EndRectTracking() terminates tracking and removes the rectangle. The initial rectangle, rect, is specified in the BView's coordinate system.

This function supports two kinds of tracking, depending on the constant passed as the how argument:

Tracking is typically initiated from within a BView's MouseDown() function and is terminated in MouseUp()

Initiates a drag-and-drop session.

message, is a BMessage object that bundles the information that will be dragged and dropped on the destination view. The caller retains responsibility for this object and can delete it after DragMessage() returns (the BView makes a copy of the message).

image, is a bitmap that the user can drag. The bitmap is automatically freed when the message is dropped.

Note

1 bit-per-pixel bitmaps aren't supported; you should avoid using them.

point locates the hotspot within image (in the bitmap's coordinate system). This is the point that's aligned with the location passed to MouseDown() or returned by GetMouse().

rect defines the dimensions of an outline rectangle that you can instead of a bitmap. The rectangle is stated in the BView's coordinate system.

replyTarget, names the object that you want to handle a message that might be sent in reply to the dragged message. If replyTarget is NULL, as it is by default, any reply that's received will be directed to the BView object that initiated the drag-and-drop session.

dragMode defines the drawing_mode which will be used to draw image as the image is dragged around. This is provided primarily so that transparent or partially transparent images can be dragged around (using the B_OP_ALPHA drawing mode).

This function works only for BView objects that are attached to a window.

Provides the location of the cursor and the state of the mouse buttons. The position of the cursor is recorded in the variable referred to by cursor; it's provided in the BView's own coordinates. A bit is set in the variable referred to by buttons for each mouse button that's down. This mask may be 0 (if no buttons are down) or it may contain one or more of the following constants:

• B_PRIMARY_MOUSE_BUTTON

• B_SECONDARY_MOUSE_BUTTON

• B_TERTIARY_MOUSE_BUTTON

The cursor doesn't have to be located within the view for this function to work; it can be anywhere on-screen. However, the BView must be attached to a window.

If the checkQueue flag is set to false, GetMouse() provides information about the current state of the mouse buttons and the current location of the cursor.

If checkQueue is true, as it is by default, this function first looks in the message queue for any pending reports of mouse-moved or mouse-up events. If it finds any, it takes the one that has been in the queue the longest (the oldest message), removes it from the queue, and reports the cursor location and button states that were recorded in the message. Each GetMouse() call removes another message from the queue. If the queue doesn't hold any B_MOUSE_MOVED or B_MOUSE_UP messages, GetMouse() reports the current state of the mouse and cursor, just as if checkQueue were false.

If checkQueue is true, and the view's parent window has pending update events, GetMouse() causes those update events to be processed.

You shouldn't use this function to track the mouse; implement the MouseMoved() function instead.

See also: modifiers()

Makes the BView the current focus view for its window (if the focused flag is true), or causes it to give up that status (if focused is false). The focus view is the view that displays the current selection and is expected to handle reports of key-down events when the window is the active window. There can be no more than one focus view per window at a time.

When called to make a BView the focus view, this function invokes MakeFocus() for the previous focus view, passing it an argument of false. It's thus called twice—once for the new and once for the old focus view.

Calling MakeFocus() is the only way to make a view the focus view; the focus doesn't automatically change on mouse-down events. BViews that can display the current selection (including an insertion point) or that can accept pasted data should call MakeFocus()in their MouseDown() functions.

A derived class can override MakeFocus() to add code that takes note of the change in status. For example, a BView that displays selectable data may want to highlight the current selection when it becomes the focus view, and remove the highlighting when it's no longer the focus view. A BView that participates in the keyboard navigation system should visually indicate that it can be operated from the keyboard when it becomes the focus view, and remove that indication when the user navigates to another view and it's notified that it's no longer the focus view.

If the BView isn't attached to a window, this function has no effect.

See also: BWindow::CurrentFocus(), IsFocus()

Returns a BScrollBar object that scrolls the BView (that has the BView as its target). The requested scroll bar has the posture orientation—B_VERTICAL or B_HORIZONTAL. If the BView isn't the target of a scroll bar with the specified orientation, this function returns NULL.

See also: BScrollBar::SetTarget()

These functions scroll the contents of the view, provided that the BView is attached to a window.

ScrollBy() adds horizontal to the left and right components of the BView's bounds rectangle, and vertical to the top and bottom components. This serves to shift the display horizontal coordinate units to the left and vertical units upward. If horizontal and vertical are negative, the display shifts in the opposite direction.

ScrollTo() shifts the contents of the view as much as necessary to put point—or (x, y)—at the upper left corner of its bounds rectangle. The point is specified in the BView's coordinate system.

Anything in the view that was visible before scrolling and also visible afterwards is automatically redisplayed at its new location. The remainder of the view is invalidated, so the BView's Draw() function will be called to fill in those parts of the display that were previously invisible. The update rectangle passed to Draw() will be the smallest possible rectangle that encloses just these new areas. If the view is scrolled in only one direction, the update rectangle will be exactly the area that needs to be drawn.

If the BView is the target of scroll bars, ScrollBy() and ScrollTo() notify the BScrollBar objects of the change in the display so they can update themselves to match. If the contents were scrolled horizontally, they call the horizontal BScrollBar's SetValue() function and pass it the new value of the left side of the bounds rectangle. If they were scrolled vertically, they call SetValue() for the vertical BScrollBar and pass it the new value of the top of the bounds rectangle.

The inline version of ScrollTo() works by creating a BPoint object and passing it to the version that's declared virtual. Therefore, if you want to override either function, you should override the virtual version. (However, due to the peculiarities of C++, overriding any version of an overloaded function hides all versions of the function. For continued access to the nonvirtual version without explicitly specifying the "BView::" prefix, simply copy the inline code from interface/View.h into the derived class.)

SetEventMask() lets you extend the scope of the mouse and keyboard events that the view can receive. If events includes B_POINTER_EVENTS, the view will receive mouse events (aka pointer events) even when the mouse isn't over the view; if it includes B_KEYBOARD_EVENTS, the view will receive keyboard events even if the view isn't in focus. (We'll look at the options argument below).

SetMouseEventMask() does the same thing as SetEventMask(), except (1) it can only be called from within an implementation of MouseDown(), and (2) the new events value—which is added to the current event mask—is only in effect until (and including) the following mouse up event. When the mouse is released, the view's previous event mask (as set through SetEventMask()) is re-established.

The option arguments lets you request other event-handling modifications (note that SetEventMask() only accepts the first of these options; SetMouseEventMask() accepts all three):

Note

To ask for an option without changing the event mask (or mouse event mask), pass 0 as the events argument.

Note

Both SetEventMask() and SetMouseEventMask() require that the view be attached to a window; they have no effect if the view isn't already attached.

EventMask() returns the view's event mask as set through SetEventMask(). It doesn't consider the mask set in SetMouseEventMask().

These functions move the pen (without drawing a line) and report the current pen location.

MovePenBy() moves the pen horizontal coordinate units to the right and vertical units downward. If horizontal or vertical are negative, the pen moves in the opposite direction. MovePenTo() moves the pen to point—or to (x, y)—in the BView's coordinate system.

Some drawing functions also move the pen—to the end of whatever they draw. In particular, this is true of StrokeLine(), DrawString(), and DrawChar(). Functions that stroke a closed shape (such as StrokeEllipse()) don't move the pen.

The pen location is a parameter of the BView's graphics environment, which is maintained by both the Application Server and the BView. If the BView doesn't belong to a window, MovePenTo() and MovePenBy() cache the location, so that later, when the BView becomes attached to a window, it can be handed to the server to become the operable pen location for the BView. If the BView belongs to a window, these functions alter both the server parameter and the client-side cache.

PenLocation() returns the point where the pen is currently positioned in the BView's coordinate system. Because of the cache, this shouldn't entail contacting the server. The default pen position is (0.0, 0.0).

See also: SetPenSize()

Saves and restores the state from the state stack. A state consists of the following: local and global origins, local and global scales, drawing mode, line cap and join modes, miter limit, pen size and location, foreground and background color, stipple pattern, local and global clipping regions, and the font context. When a state is saved to the stack, a new state context is created, with a local scale of zero, a local origin at (0,0), and no clipping region.

Warning

If the BView isn't attached to a window, these functions will crash the application.

These methods implement support for PostScript-style line cap and join modes. The cap mode determines the shape of the endpoints of stroked paths, while the join mode determines the shape of the corners of the paths (i.e. where two lines meet).

The following values of cap_mode are defined:

Additionally, the following values of join_mode are defined:

SetLineMode() sets the line and join modes and the miter limit while LineCapMode(), LineJoinMode(), and LineMiterLimit() return them. The line mode affects all of the Stroke…() methods except for Arc, Ellipse, and RoundRect.

Scales the coordinate system the view uses for drawing. The default scale is 1.0; smaller ratio values reduce the size of the drawing coordinate system; larger numbers magnify the system. For example, a ratio of 0.5 makes a subsequent drawing twice as small and moves the drawing closer to the origin, and 2.0 makes it twice as big and moves it away, as shown below.

Note

The scaling ratio only affects subsequent drawing operations! Changing the scale doesn't affect the graphics already displayed in the view, the view's frame rectangle and clipping region, the placement and size of subviews, translation of mouse coordinates to and from view space, and so forth.

Multiple SetScale() calls don't compound within the same graphics state, but they do compound across pushed states:

aview->SetScale(0.5);
aview->SetScale(0.5);
/* aview's scaling is 0.5. */

bview->SetScale(0.5);
bview->PushState();
bview->SetScale(0.5);
/* view's scaling is 0.25. */

Warning

The BView must be attached to a window before you call this function.

SetPenSize() sets the size of the BView's pen—the graphics parameter that determines the thickness of stroked lines—and PenSize() returns the current pen size. The pen size is stated in coordinate units, but is translated to a device-specific number of pixels for each output device.

The pen tip can be thought of as a brush that's centered on the line path and held perpendicular to it. If the brush is broader than one pixel, it paints roughly the same number of pixels on both sides of the path.

The default pen size is 1.0 coordinate unit. It can be set to any nonnegative value, including 0.0. If set to 0.0, the size is translated to one pixel for all devices. This guarantees that it will always draw the thinnest possible line no matter what the resolution of the device.

Thus, lines drawn with pen sizes of 1.0 and 0.0 will look alike on the screen (one pixel thick), but the line drawn with a pen size of 1.0 will be 1/72 of an inch thick when printed, however many printer pixels that takes, while the line drawn with a 0.0 pen size will be just one pixel thick.

The pen size is a parameter of the BView's graphics environment maintained by the Application Server and cached by the BView. If the BView isn't attached to a window, SetPenSize() records the size so that later, when the BView is added to a window and becomes known to the server, the cached value can automatically be established as the operable pen size for the BView. If the BView belongs to a window, this function changes both the server and the cache.

See also: "The Pen" in the chapter overview, StrokeArc(), MovePenBy()

These functions set and return the current high and low colors of the BView. These colors combine to form a pattern that's passed as an argument to the Stroke…() and Fill…() drawing functions. The B_SOLID_HIGH pattern is the high color alone, and B_SOLID_LOW is the low color alone.

The default high color is black—red, green, and blue values all equal to 0. The default low color is white—red, green, and blue values all equal to 255.

The inline versions of SetHighColor() and SetLowColor() take separate arguments for the red, blue, and green color components; they work by creating an rgb_color data structure and passing it to the corresponding function that's declared virtual. Therefore, if you want to override either function, you should override the virtual version. (However, due to the peculiarities of C++, overriding any version of an overloaded function hides all versions of the function. For continued access to the nonvirtual version without explicitly specifying the "BView::" prefix, simply copy the inline code from interface/View.h into the derived class.)

The high and low colors are parameters of the BView's graphics environment, which is kept in the BView's shadow counterpart in the Application Server and cached in the BView. If the BView isn't attached to a window, SetHighColor() and SetLowColor() cache the color value so that later, when the BView is placed in a window and becomes known to the server, the cached value can automatically be registered as the current high or low color for the view. If the BView belongs to a window, these functions alter both the client-side and the server-side values.

HighColor() and LowColor() return the BView's current high and low colors. Because of the cache, this shouldn't entail contacting the Application Server.

See also: "Patterns" "in the Drawing" section of this chapter, SetViewColor()

These functions set and return the view's background color. This is the color that's displayed when a view is erased during an update, or when the view is resized to expose new areas. The default view color is white (255,255,255). If you don't want the view to be erased in an update, set the view color to B_TRANSPARENT_COLOR. (Despite the name this doesn't actually make the view transparent.)

The inline version of SetViewColor() calls the virtual version. Thus, overriding the virtual version affects both versions. However, due to the peculiarities of C++, overriding any version of an overloaded function hides all versions of the function. To fix this, simply copy the inline code from View.h into your subclass.

ViewColor() returns the current background color.

See also: "The View Color" in the "Drawing" section of this chapter, SetHighColor(), SetViewBitmap()

These two functions set and retrieve the graphics state variables which control the details of alpha transparency drawing. These variables will have an effect on drawing in the view only if the drawing mode has been set to B_OP_ALPHA by SetDrawingMode().

alphaSrcMode is one of the following two constants, with associated meanings:

alphaFncMode is one of the following two constants, with associated meanings:

These functions set and return the BView's drawing mode, which can be any of the following eleven constants:

• B_OP_COPY

• B_OP_OVER

• B_OP_ERASE

• B_OP_INVERT

• B_OP_SELECT

• B_OP_ALPHA

• B_OP_MIN

• B_OP_MAX

• B_OP_ADD

• B_OP_SUBTRACT

• B_OP_BLEND

The drawing mode is an element of the BView's graphics environment, which both the Application Server and the BView keep track of. If the BView isn't attached to a window, SetDrawingMode() caches the mode. When the BView is placed in a window and becomes known to the server, the cached value is automatically set as the current drawing mode. If the BView belongs to a window, SetDrawingMode() makes the change in both the server and the cache.

DrawingMode() returns the current mode. Because of the cache, this generally doesn't entail a trip to the server.

The default drawing mode is B_OP_COPY. It and the other modes are explained under "Drawing Modes" in the "Drawing" section of this chapter.

ForceFontAliasing() is used in conjunction with printing. When called with a value of true, if causes subsequent printing to be done without antialiasing printed characters. This is normally what is desired with high-resolution printers, to guarantee that the edges of printed characters appear sharp. Calling ForceFontAliasing() with an argument of false turns antialiasing back on, which may be desirable with lower-resolution printers.

Note that ForceFontAliasing() does not affect characters or strings drawn to the screen.

See also: The BPrintJob class.

Gets the height of the BView's font. This function provides the same information as BFont's GetHeight(). The following code

font_height height;
myView->GetFontHeight(&height);

is equivalent to:

font_height height;
BFont font;
myView->GetFont(&font);
font.GetHeight(&height);

See the BFont class for more information.

SetFont() sets the BView's current font so that it matches the specified properties of the font BFont object. The properties mask is formed by combining the following constants:

• B_FONT_FAMILY_AND_STYLE

• B_FONT_SPACING

• B_FONT_SIZE

• B_FONT_ENCODING

• B_FONT_SHEAR

• B_FONT_FACE

• B_FONT_ROTATION

• B_FONT_FLAGS

Each constant corresponds to a settable property of the BFont object. The default mask, B_FONT_ALL, is a shorthand for all the properties (including any that might be added in future releases). If the mask is 0, SetFont() won't set the BView's font.

GetFont() copies the BView's current font to the BFont object passed as an argument. Modifying this copy doesn't modify the BView's font; it takes an explicit SetFont() call to affect the BView.

For example, this code changes the size of a BView's font and turns antialiasing off:

BFont font;
myView->GetFont(&font);
font.SetSize(67.0);
font.SetFlags(B_DISABLE_ANTIALIASING);
myView->SetFont(&font, B_FONT_SIZE | B_FONT_FLAGS);

Since the BFont object that this example code alters is a copy of the BView's current font, it's not strictly necessary to name the properties that are different when calling SetFont(). However, it's more efficient and better practice to do so.

The font is part of the BView's graphic environment. Like other elements in the environment, it can be set whether or not the BView is attached to the window. Graphics parameters are kept by the Application Server and also cached by the BView object.

See also: get_font_family()

Sets the size of the BView's font to points. This function is a shorthand for a SetFont() call that just alters the font size. For example, this line of code

myView->SetFontSize(12.5);

does the same thing as:

BFont font;
font.SetSize(12.5);
myView->SetFont(&font, B_FONT_SIZE);

See also: the BFont class

These functions measure how much room is required to draw a string, or a group of strings, in the BView's current font. They're equivalent to the identically named set of functions defined in the BFont class, except that they assume the BView's font. For example, this line of code

float width;
width = myView->StringWidth("Be"B_UTF8_REGISTERED);

produces the same result as:

float width;
BFont font;
myView->GetFont(&font);
width = font.StringWidth("Be"B_UTF8_REGISTERED);

See also: BFont::StringWidth(), BFont::GetEscapements()

Truncates the BString inOutString to be no wider than width pixels. The mode flags control how the string is truncated.

Modifies the view's clipping region by intersecting the current clipping region with the pixels drawn by picture (in the case of ClipToPicture()) or with everything outside the pixels drawn by picture (in the case of ClipToInversePicture()), to produce the new clipping region.

Note that BPicture instances are, by their nature, resolution independent; when the ClipToPicture() or ClipToInversePicture() command is invoked, picture is effectively drawn at the same resolution as the invoking view, and the bitmap produced by that action is used to modify the clipping region. You may think of picture as executing its drawing instructions on a surface that starts out as completely transparent; at the end of the process, each pixel on the drawing surface will either be either completely transparent, or will be at least somewhat opaque. The pixels which are at least somewhat opaque are those which were "drawn" by picture.

If sync is false, the functions will execute asynchronously; normally they execute synchronously (i.e. wait for the drawing actions to be completed by the Application Server.)

See also: BeginPicture()

Restricts the drawing that the BView can do to region.

The Application Server keeps track of a clipping region for each BView that's attached to a window. It clips all drawing the BView does to that region; the BView can't draw outside of it.

By default, the clipping region contains only the visible area of the view and, during an update, only the area that actually needs to be drawn. By passing a region to this function, an application can further restrict the clipping region. When calculating the clipping region, the server intersects it with the region provided. The BView can draw only in areas common to the region passed and the clipping region as the server would otherwise calculate it. The region passed can't expand the clipping region beyond what it otherwise would be.

The clipping region is additionally affected by any items on the state stack. If any saved states contain clipping regions, then the actual clipping region used by the Application Server is the intersection of the local clipping region (as set by this method) and the regions stored on the state stack.

If called during an update, ConstrainClippingRegion() restricts the clipping region only for the duration of the update.

Calls to ConstrainClippingRegion() are not additive; each region that's passed replaces the one that was passed in the previous call. Passing a NULL pointer removes the previous region without replacing it. The function works only for BViews that are attached to a window.

See also: Draw()

Modifies the BRegion object passed as an argument so that it describes the current local clipping region of the BView, the region where the BView is allowed to draw. It's most efficient to allocate temporary BRegions on the stack:

BRegion clipper;
GetClippingRegion(&clipper);
. . .

Ordinarily, the clipping region is the same as the visible region of the view, the part of the view currently visible on-screen. The visible region is equal to the view's bounds rectangle minus:

• The frame rectangles of its children,

• Any areas that are clipped because the view doesn't lie wholly within the frame rectangles of all its ancestors in the view hierarchy, and

• Any areas that are obscured by other windows or that lie in a part of the window that's off-screen.

The clipping region can be smaller than the visible region if the program restricted it by calling ConstrainClippingRegion(). It will exclude any area that doesn't intersect with the region passed to ConstrainClippingRegion().

The clipping region is additionally modified by any items on the state stack. If any saved states contain clipping regions, then the actual clipping region used by the Application Server is the intersection of the local clipping region (as set by ConstrainClippingRegion()) and the regions stored on the state stack.

While the BView is being updated, the clipping region contains just those parts of the view that need to be redrawn. This may be smaller than the visible region, or the region restricted by ConstrainClippingRegion(), if:

• The update occurs during scrolling. The clipping region will exclude any of the view's visible contents that the Application Server is able to shift to their new location and redraw automatically.

• The view rectangle has grown (because, for example, the user resized the window larger) and the update is needed only to draw the new parts of the view.

• The update was caused by Invalidate() and the rectangle passed to Invalidate() didn't cover all of the visible region.

• The update was necessary because CopyBits() couldn't fill all of a destination rectangle.

If, while updating is ongoing, you call the view's parent's GetClippingRegion() function, the resulting region indicates only the area of that view that requries updating, and so forth. In other words, this change in behavior (from returning the true clipping region to returning the update region) is recursive up the view hierarchy.

This function works only if the BView is attached to a window. Unattached BViews can't draw and therefore have no clipping region.

See also: ConstrainClippingRegion(), Draw(), Invalidate()

These functions place a bitmap image in the view at the current pen position, at the point specified, or within the designated destination rectangle. The point and the destination rectangle are stated in the BView's coordinate system.

If a source rectangle is given, only that part of the bitmap image is drawn. Otherwise, the entire bitmap is placed in the view. The source rectangle is stated in the internal coordinates of the BBitmap object.

If the source image is bigger than the destination rectangle, it's scaled to fit.

The two functions differ in only one respect: DrawBitmap() waits for the Application Server to finish rendering the image before it returns. DrawBitmapAsync() doesn't wait; it passes the image to the server and returns immediately. The latter function can be more efficient in some cases—for example, you might use an asynchronous function to draw several bitmaps and then call Sync() to wait for them all to finish rather than wait for each one individually:

DrawBitmapAsync(bitmapOne, firstPoint);
DrawBitmapAsync(bitmapTwo, secondPoint);
DrawBitmapAsync(bitmapThree, thirdPoint);
Sync();

Or, if you can cram some useful work between the time you send the bitmap to the Application Server and the time you need to be sure that it has appeared on-screen, DrawBitmapAsync() will free your thread to do that work immediately:

DrawBitmapAsync(someBitmap, somePoint);
/* do something else */
Sync();

See also: The "Drawing" in the chapter overview, the BBitmap class

Draws the character c at the current pen position—or at the point specified—and moves the pen to a position immediately to the right of the character. This function is equivalent to passing a string of one character to DrawString(). The point is specified in the BView's coordinate system.

Draws the characters encoded in length bytes of string—or, if the number of bytes isn't specified, all the characters in the string, up to the null terminator ('\0'). Characters are drawn in the BView's current font. The font's direction determines whether the string is drawn left-to-right or right-to-left. Its rotation determines the angle of the baseline (horizontal for an unrotated font). The spacing mode of the font determines how characters are positioned within the string and the string width.

This function places the characters on a baseline that begins one pixel above the current pen position—or one pixel above the specified point in the BView's coordinate system. It draws the characters to the right (assuming an unrotated font) and moves the pen to the baseline immediately past the characters drawn. For a left-to-right font, the pen will be in position to draw the next character, as shown below:

The characters are drawn in the opposite direction for a right-to-left font, but the pen still moves left-to-right:

Note

The BeOS draws text one pixel above the logical baseline to maintain compatibility with an earlier version of one of our most commonly-used font rasterizers. This affects both fonts and BShapes representing glyphs (see BFont::GetGlyphShapes(). To draw text at the right place, add one to the Y coordinate when calling MovePenTo() or specifying a BPoint at which to begin drawing.

For a font that's read from left-to-right, a series of simple DrawString() calls (with no point specified) will produce a continuous string. For example, these two lines of code,

DrawString("tog");
DrawString("ether");

will produce the same result as this one,

DrawString("together");

except if the spacing mode is B_STRING_SPACING. Under B_STRING_SPACING, character placements are adjusted keeping the string width constant. The adjustments are contextually dependent on the string and may therefore differ depending on whether there are two strings ("tog" and "ether") or just one ("together").

If a delta argument is provided, DrawString() adds the additional amounts specified in the escapement_delta structure to the width of each character. This structure has two fields:

When drawing to the screen, DrawString() uses antialiasing—unless the BView's font disables it or the font size is large enough (over 1,000.0 points) so that its benefits aren't required. Antialiasing produces colors at the margins of character outlines that are intermediate between the color of the text (the BView's high color) and the color of the background against which the text is drawn. When drawing in B_OP_COPY mode, antialiasing requires the BView's low color to match the background color.

It's much faster to draw a string in B_OP_COPY mode than in any other mode. If you draw the same string repeatedly in the same location in B_OP_OVER mode without erasing, antialiasing will produce different, and worse, results each time as the intermediate color it previously produced is treated as the new background each time. Antialiasing doesn't produce pleasing results in B_OP_SELECT mode.

This is a graphical drawing function, so any character that doesn't have an escapement or a visible representation (including white space) is replaced by an undefined character that can be drawn (currently an empty box). This includes all control characters (those with values less than B_SPACE, 0x20).

DrawString() doesn't erase before drawing.

See also: MovePenBy(), SetFont(), the BFont class

Fills the region with the pattern specified by aPattern—or, if no pattern is specified, with the current high color. Filling a region is equivalent to filling all the rectangles that define the region.

See also: The BRegion class

These functions draw a third degree Bezier curve. StrokeBezier() strokes a line along the path of the curve; the width of the line is determined by the current pen size. FillBezier() fills in the region defined by the path of the curve and the line joining the two endpoints.

controlPoints points to an array of the four points for the curve. Both functions draw using the pattern specified by aPattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: StrokeEllipse(), SetPenSize(), StrokeRoundRect()

These functions draw all or part of the ellipse that's inscribed in rect or that has its center at center and has horizontal and vertical radii xRadius and yRadius. The ellipse is always aligned with the x and y axes. A more flexible curve-drawing mechanism is given by StrokeBezier() and FillBezier().

StrokeEllipse() strokes a line around the entire perimeter of the ellipse and FillEllipse() fills the area the ellipse encloses.

StrokeArc() and FillArc() stroke and fill a section of the ellipse, starting at angle (where 0 ° points right along the x-axis) and proceeding (counterclockwise) span degrees. In the illustration below, the red arc is the result of StrokeArc() with an angle of 10° and span of 235°; the blue area is the same arc filled through FillArc(). The center of the ellipse (the yellow dot) is drawn for reference.

Warning

Currently, angle and span measurements in fractions of a degree are not supported.

For the stroking functions, the width of the stroked line is determined by the current pen size. All functions draw using aPattern or, if no pattern is specified, the current high color. The functions neither depend on nor alter the current pen position.

Draws a straight line between the start and end points—or, if no starting point is given, between the current pen position and end point—and leaves the pen at the end point.

This function draws the line using the current pen size and the specified pattern. If no pattern is specified, the line is drawn in the current high color. The points are specified in the BView's coordinate system.

See also: SetPenSize() BeginLineArray()

These functions draw a polygon with an arbitrary number of sides. StrokePolygon() strokes a line around the edge of the polygon using the current pen size. If a pointList is specified rather than a BPolygon object, this function strokes a line from point to point, connecting the first and last points if they aren't identical. However, if the isClosed flag is false, StrokePolygon() won't stroke the line connecting the first and last points that define the BPolygon (or the first and last points in the pointList). This leaves the polygon open—making it not appear to be a polygon at all, but rather a series of straight lines connected at their end points. If isClosed is true, as it is by default, the polygon will appear to be a polygon, a closed figure.

FillPolygon() is a simpler function; it fills in the entire area enclosed by the polygon.

Both functions must calculate the frame rectangle of a polygon constructed from a point list—that is, the smallest rectangle that contains all the points in the polygon. If you know what this rectangle is, you can make the function somewhat more efficient by passing it as the rect parameter.

Both functions draw using the specified pattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: SetPenSize()

These functions draw a rectangle. StrokeRect() strokes a line around the edge of the rectangle; the width of the line is determined by the current pen size. FillRect() fills in the entire rectangle.

Both functions draw using the pattern specified by aPattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: SetPenSize(), StrokeRoundRect()

These functions draw a rectangle with rounded corners. The corner arc is one-quarter of an ellipse, where the ellipse would have a horizontal radius equal to xRadius and a vertical radius equal to yRadius.

Except for the rounded corners of the rectangle, these functions work exactly like StrokeRect() and FillRect().

Both functions draw using the pattern specified by aPattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: StrokeEllipse()

These functions draw a shape. StrokeShape() strokes a line around the edge of the shape; the width of the line is determined by the current pen size. FillShape() fills in the entire shape.

Both functions draw using the pattern specified by aPattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: SetPenSize()

These functions draw a triangle, a three-sided polygon. StrokeTriangle() strokes a line the width of the current pen size from the first point to the second, from the second point to the third, then back to the first point. FillTriangle() fills in the area that the three points enclose.

Each function must calculate the smallest rectangle that contains the triangle. If you know what this rectangle is, you can make the function marginally more efficient by passing it as the rect parameter.

Both functions do their drawing using the pattern specified by aPattern—or, if no pattern is specified, in the current high color. Neither function alters the current pen position.

See also: SetPenSize()

These functions provide a more efficient way of drawing a large number of lines than repeated calls to StrokeLine(). BeginLineArray() signals the beginning of a series of up to count AddLine() calls; EndLineArray() signals the end of the series. Each AddLine() call defines a line from the start point to the end point, associates it with a particular color, and adds it to the array. The lines can each be a different color; they don't have to be contiguous. When EndLineArray() is called, all the lines are drawn—using the then current pen size—in the order that they were added to the array.

These functions don't change any graphics parameters. For example, they don't move the pen or change the current high and low colors. Parameter values that are in effect when EndLineArray() is called are the ones used to draw the lines. The high and low colors are ignored in favor of the color specified for each line.

The count passed to BeginLineArray() is an upper limit on the number of lines that can be drawn. Keeping the count close to accurate and within reasonable bounds helps the efficiency of the line-array mechanism. It's a good idea to keep it less than 256; above that number, memory requirements begin to impinge on performance.

See also: StrokeLine()

BeginPicture() starts a new "picture recording" session: Subsequent drawing instructions invoked upon the view are recorded in the BPicture argument. AppendToPicture() does the same, but doesn't clear the argument first—it tacks additional instructions on to the end of the BPicture. EndPicture() ends the recording session; it returns the object that was passed to BeginPicture() or AppendToPicture().

While it's recording a picture, the BView doesn't display anything to the screen. To render the drawing, you use the DrawPicture() function.

The picture captures only primitive graphics operations such as DrawString(), FillArc(), and SetFont(). Furthermore, only instructions performed by this view are recorded; the drawing done by the view's children is not recorded.

A BPicture can be recorded only if the BView is attached to a window. The window can be off-screen and the view itself can be hidden or reside outside the current clipping region.

Copies the image displayed in the source rectangle to the destination rectangle, where both rectangles lie within the view and are stated in the BView's coordinate system.

If the two rectangles aren't the same size, the source image is scaled to fit.

If not all of the destination rectangle lies within the BView's visible region, the source image is clipped rather than scaled.

If not all of the source rectangle lies within the BView's visible region, only the visible portion is copied. It's mapped to the corresponding portion of the destination rectangle. The BView is then invalidated so its Draw() function will be called to update the part of the destination rectangle that can't be filled with the source image.

The BView must be attached to a window.

Draws the previously recorded picture at the current pen position—or at the specified point in the BView's coordinate system. The point or pen position is taken as the coordinate origin for all the drawing instructions recorded in the BPicture. The last form of the method plays a picture from an arbitrary offset of a file.

The two functions differ in only one respect: DrawPicture() waits for the Application Server to finish rendering the image before it returns. DrawPictureAsync() doesn't wait; it passes the image to the server and returns immediately. The latter function can be more efficient in some cases—for example, you might use an asynchronous function to draw several bitmaps and then call Sync() to wait for them all to finish rather than wait for each one individually:

Nothing that's done in the BPicture can affect anything in the BView's graphics state—for example, the BPicture can't reset the current high color or the pen position. Conversely, nothing in the BView's current graphics state affects the drawing instructions captured in the picture. The graphics parameters that were in effect when the picture was recorded determine what the picture looks like.

See also: BeginPicture()

These functions flush the window's connection to the Application Server. If the BView isn't attached to a window, Flush() does nothing.

Warning

If the BView isn't attached to a window, Sync() will crash the application.

For reasons of efficiency, the window's connection to the Application Server is buffered. Drawing instructions destined for the server are placed in the buffer and dispatched as a group when the buffer becomes full. Flushing empties the buffer, sending whatever it contains to the server, even if it's not yet full.

The buffer is automatically flushed on every update. However, if you do any drawing outside the update mechanism—in response to interface messages, for example—you need to explicitly flush the connection so that drawing instructions won't languish in the buffer while waiting for it to fill up or for the next update. You should also flush it if you call any drawing functions from outside the window's thread.

Flush() simply flushes the buffer and returns. It does the same work as BWindow's function of the same name.

Sync() flushes the connection, then waits until the server has executed the last instruction that was in the buffer before returning. This alternative to Flush() prevents the application from getting ahead of the server (ahead of what the user sees on-screen) and keeps both processes synchronized.

It's a good idea, for example, to call Sync(), rather than Flush(), after employing BViews to produce a bitmap image (a BBitmap object). Sync() is the only way you can be sure the image has been completely rendered before you attempt to draw with it.

(Note that all BViews attached to a window share the same connection to the Application Server. Calling Flush() or Sync() for any one of them flushes the buffer for all of them.)

Invalidates the rect portion of the view, causing update messages—and consequently Draw() notifications—to be generated for the BView and all descendants that lie wholly or partially within the rectangle. The rectangle is stated in the BView's coordinate system.

If no rectangle is specified, the BView's entire bounds rectangle is invalidated.

Since only BViews that are attached to a window can draw, only attached BViews can be invalidated.

See also: Draw(), GetClippingRegion(), BWindow::UpdateIfNeeded()

Inverts all the colors displayed within the rect rectangle. A subsequent InvertRect() call on the same rectangle restores the original colors. This operation can be used to "highlight" a selection made as the user drags the mouse.

The rectangle is stated in the BView's coordinate system.

See also: BScreen::ColorMap()

SetViewBitmap() sets the background bitmap for the view. The view bitmap is a background image for the view; all drawing in the view occurs over this bitmap. The background color is used to fill in the visible regions not covered by the background bitmap.

The background bitmap is passed in bitmap. The caller can delete bitmap after the function returns.

If a source rectangle is given, only that part of the bitmap is used. Otherwise, the entire bitmap is used as the background bitmap. The destination rectangle, if given, specifies the placement of the bitmap in the view. It need not be the same size as the source rectangle; scaling is performed automatically by the application server. If no destination is given, the image will be placed, unscaled, at the upper left corner of the view.

follow determines the behavior of destination as the view is resized; see the BView constructor for specifics. options specifies additional view options. Currently, only one option, B_TILE_BITMAP, is defined. If set, the view bitmap is tiled across the view.

ClearViewBitmap() clears the background bitmap for the view.

See also: "The Background Bitmap" in the "Drawing" section of this chapter, SetViewColor()

SetViewOverlay() sets the overlay bitmap for the view. The overlay bitmap is superimposed on top of the view's contents. The colorKey is used to determine which color in the overlay should be treated as transparent, allowing the view's contents to be visible.

The overlay bitmap is passed in bitmap. The caller can delete bitmap after the function returns.

If a source rectangle is given, only that part of the bitmap is used. Otherwise, the entire bitmap is used as the overlay bitmap. The destination rectangle, if given, specifies the placement of the overlay bitmap in the view. It need not be the same size as the source rectangle; scaling is performed automatically by the application server. If no destination is given, the image will be placed, unscaled, at the upper left corner of the view.

follow determines the behavior of destination as the view is resized; see the BView constructor for specifics. options specifies additional view options. The same options allowed by SetViewBitmap() are allowed here.

Note

You can't use both a background bitmap and an overlay in the same view.

ClearViewOverlay() clears the overlay bitmap for the view.

Returns a new BView object, allocated by new and created with the version of the constructor that takes a BMessage archive. However, if the message doesn't contain archived data for a BView, Instantiate() returns NULL.

See also: BArchivable::Instantiate(), instantiate_object()