API Documentation

BView

BView

Constructor and Destructor

BView()

BView::BView(BRect frame, const char *name, uint32 resizingMode, uint32 flags)
BView::BView(BMessage *archive)

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:

Constant

Description

B_WILL_DRAW

Indicates that the BView does some drawing of its own and therefore can’t be ignored when the window is updated. If this flag isn’t set, the BView won’t receive update notifications—its Draw() function won’t be called—and it won’t be erased to its background view color if the color is other than white.

B_PULSE_NEEDED

Indicates that the BView should receive Pulse() notifications.

B_FRAME_EVENTS

Indicates that the BView should receive FrameResized() and FrameMoved() notifications when its frame rectangle changes—typically as a result of the automatic resizing behavior described above. FrameResized() is called when the dimensions of the view change; FrameMoved() is called when the position of its left top corner in its parent’s coordinate system changes.

B_FULL_UPDATE_ON_RESIZE

Indicates that the entire view should be updated when it’s resized. If this flag isn’t set, only the portions that resizing adds to the view will be included in the clipping region. This doesn’t affect the view’s children; their own flags determine when updates will occur.

B_NAVIGABLE

Indicates that the BView can become the focus view for keyboard actions. This flag makes it possible for the user to navigate to the view and put it in focus by pressing the Tab key. See “Keyboard Navigation” at the beginning of this chapter.

B_NAVIGABLE_JUMP

Marks the position of a group of views for keyboard navigation. By pressing Control+Tab, the user can jump from group to group. The focus lands on the first BView in the group that has the B_NAVIGABLE flag set. This may be the same BView that has the B_NAVIGABLE_JUMP marker, or the B_NAVIGABLE_JUMP BView may be the parent of a group of B_NAVIGABLE views.

B_SUBPIXEL_PRECISE

Instructs the rendering methods to use subpixel precision when drawing. If you don’t set this flag, coordinates are rounded to the nearest unit.

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()

~BView()

virtual BView::~BView()

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.

Hook Functions

AttachedToWindow(), AllAttached()

virtual void BView::AttachedToWindow()

virtual void BView::AllAttached()

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()

DetachedFromWindow(), AllDetached()

virtual void BView::DetachedFromWindow()

virtual void BView::AllDetached()

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.

Draw()

virtual void BView::Draw(BRect updateRect)

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()

DrawAfterChildren()

virtual void BView::DrawAfterChildren(BRect updateRect)

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().

FrameMoved()

virtual void BView::FrameMoved(BPoint newLocation)

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()

FrameResized()

virtual void BView::FrameResized(float width, float height)

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(), ResizeToPreferred()

virtual void BView::GetPreferredSize(float *width, float *height)

virtual void BView::ResizeToPreferred()

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()

KeyDown()

virtual void BView::KeyDown(const char *bytes, int32 numBytes)

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()

KeyUp()

virtual void BView::KeyUp(const char *bytes, int32 numBytes)

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.

MessageReceived()

virtual void BView::MessageReceived(BMessage *message)

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

MouseDown()

virtual void BView::MouseDown(BPoint point)

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.

MouseMoved()

virtual void BView::MouseMoved(BPoint point, uint32 transit, const BMessage *message)

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.

MouseUp()

virtual void BView::MouseUp(BPoint point)

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.

Pulse()

virtual void BView::Pulse()

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,

TargetedByScrollView()

virtual void BView::TargetedByScrollView(BScrollView *scroller)

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.

WindowActivated()

virtual void BView::WindowActivated(bool active)

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()

General Functions

Archive()

virtual status_t BView::Archive(BMessage *archive, bool deep = true) const

Archives the BView in the BMessage archive.

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

Bounds()

BRect BView::Bounds() const

Returns the BView’s bounds rectangle.

ConvertToParent(), ConvertFromParent()

BPoint BView::ConvertToParent(BPoint localPoint) const
void BView::ConvertToParent(BPoint *localPoint) const
BRect BView::ConvertToParent(BRect localRect) const
void BView::ConvertToParent(BRect *localRect) const

BPoint BView::ConvertFromParent(BPoint parentPoint) const
void BView::ConvertFromParent(BPoint *parentPoint) const
BRect BView::ConvertFromParent(BRect parentRect) const
void BView::ConvertFromParent(BRect *parentRect) const

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(), ConvertFromScreen()

BPoint BView::ConvertToScreen(BPoint localPoint) const
void BView::ConvertToScreen(BPoint *localPoint) const
BRect BView::ConvertToScreen(BRect localRect) const
void BView::ConvertToScreen(BRect *localRect) const

BPoint BView::ConvertFromScreen(BPoint screenPoint) const
void BView::ConvertFromScreen(BPoint *screenPoint) const
BRect BView::ConvertFromScreen(BRect screenRect) const
void BView::ConvertFromScreen(BRect *screenRect) const

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()

Frame()

BRect BView::Frame() const

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.

Hide(), Show()

virtual void BView::Hide()

virtual void BView::Show()

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()

IsFocus()

bool BView::IsFocus()

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()

IsHidden()

bool BView::IsHidden()

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.

IsPrinting()

bool BView::IsPrinting() const

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

LeftTop()

BPoint BView::LeftTop() const

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()

MoveBy(), MoveTo()

void BView::MoveBy(float horizontal, float vertical)

void BView::MoveTo(BPoint point)
void BView::MoveTo(float x, float y)

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()

ResizeBy(), ResizeTo()

void BView::ResizeBy(float horizontal, float vertical)

void BView::ResizeTo(float width, float height)

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()

SetFlags(), Flags()

virtual void BView::SetFlags(uint32 mask)

uint32 BView::Flags() const

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()

SetOrigin(), Origin()

void BView::SetOrigin(BPoint pt)
void BView::SetOrigin(float x, float y)

BPoint BView::Origin() const

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).

SetResizingMode(), ResizingMode()

virtual void BView::SetResizingMode(uint32 mode)

uint32 BView::ResizingMode() const

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()

SetViewCursor()

void BView::SetViewCursor(const BCursor *cursor, bool sync = true) const

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.

Window()

BWindow *BView::Window() const

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()

View Hierarchy Functions

AddChild(), RemoveChild()

void BView::AddChild(BView *aView, BView *sibling = NULL)

bool BView::RemoveChild(BView *aView)

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()

FindView()

BView *BView::FindView(const char *name) const

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.

Parent(), NextSibling(), PreviousSibling(), ChildAt(), CountChildren()

BView *BView::Parent() const

BView *BView::NextSibling() const

BView *BView::PreviousSibling() const

BView *BView::ChildAt(int32 index) const

int32 BView::CountChildren() const

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();
   }
}

RemoveSelf()

bool BView::RemoveSelf()

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()

Graphics State Functions

MovePenBy(), MovePenTo(), PenLocation()

void BView::MovePenBy(float horizontal, float vertical)

void BView::MovePenTo(BPoint point)
void BView::MovePenTo(float x, float y)

BPoint BView::PenLocation() const

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()

PushState(), PopState()

void BView::PushState()

void BView::PopState()

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.

SetLineMode(), LineCapMode(), LineJoinMode(), LineMiterLimit()

void BView::SetLineMode(cap_mode lineCap, join_mode lineJoin, float miterLimit = B_DEFAULT_MITER_LIMIT)

cap_mode BView::LineCapMode() const

join_mode BView::LineJoinMode() const

float BView::LineMiterLimit() const

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:

Constant

Description

B_ROUND_CAP

A semicircle is drawn around the endpoint. Its diameter is equal to the width of the line.

B_BUTT_CAP

The line is squared off and does not extend beyond the endpoint.

B_SQUARE_CAP

The line is squared off, extending past the endpoint for a distance equal to half the width of the line.

Additionally, the following values of join_mode are defined:

Constant

Description

B_ROUND_JOIN

Acts identically to B_ROUND_CAP, except applied to joins.

B_MITER_JOIN

The lines are extended until they touch. If they meet at an angle greater than 2*arcsin(1/miterLimit), a bevel join is used instead.

B_BEVEL_JOIN

Butt end caps are used at the common endpoint and the empty area between the caps is filled with a triangle.

B_BUTT_JOIN

Acts identically to B_BUTT_CAP, except applied to joins.

B_SQUARE_JOIN

Acts identically to B_SQUARE_CAP, except applied to joins.

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.

SetScale()

void BView::SetScale(float ratio)

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.

File Panel Views

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(), PenSize()

virtual void BView::SetPenSize(float size)

float BView::PenSize() const

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()

SetHighColor(), HighColor(), SetLowColor(), LowColor()

virtual void BView::SetHighColor(rgb_color color)
inline void BView::SetHighColor(uchar red, uchar green, uchar blue, uchar alpha = 255)

rgb_color BView::HighColor() const

virtual void BView::SetLowColor(rgb_color color)
inline void BView::SetLowColor(uchar red, uchar green, uchar blue, uchar alpha = 255)

rgb_color BView::LowColor() const

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()

SetViewColor(), ViewColor()

virtual void BView::SetViewColor(rgb_color color)
inline void BView::SetViewColor(uchar red, uchar green, uchar blue, uchar alpha = 255)

rgb_color BView::ViewColor() const

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()

SetBlendingMode(), GetBlendingMode()

virtual void BView::SetBlendingMode(source_alpha alphaSrcMode, alpha_function alphaFncMode)

virtual void BView::GetBlendingMode(source_alpha *alphaSrcMode, alpha_function *alphaFncMode)

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:

Constant

Description

B_CONSTANT_ALPHA

Use the alpha channel of the current high color as the transparency value for whatever is being drawn.

B_PIXEL_ALPHA

When drawing a bitmap, use the alpha value associated with each pixel as the transparency value for that pixel. This can be used to obtain some interesting variable transparency effects.

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

Constant

Description

B_ALPHA_OVERLAY

The “normal” mode, used when drawing a transparent image or shape over an opaque background.

B_ALPHA_COMPOSITE

Used when blending two or more transparent images together offscreen, to produce a new transparent image that will later be drawn onscreen using the B_ALPHA_OVERLAY setting.

SetDrawingMode(), DrawingMode()

virtual void BView::SetDrawingMode(drawing_mode mode)

drawing_mode BView::DrawingMode() const

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()

void BView::ForceFontAliasing(bool enable)

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.

GetFontHeight()

void BView::GetFontHeight(font_height *fontHeight) const

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(), GetFont()

void BView::SetFont(const BFont *font, uint32 properties = B_FONT_ALL)

void BView::GetFont(BFont *font)

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()

SetFontSize()

void BView::SetFontSize(float points)

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

StringWidth(), GetStringWidths()

float BView::StringWidth(const char *string) const
float BView::StringWidth(const char *string, int32 length) const

void BView::GetStringWidths(char *stringArray[], int32 lengthArray[], int32 numStrings, float widthArray[]) const

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()

TruncateString()

void BView::TruncateString(BString *inOutString, uint32 mode, float width) const

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

Constant

Description

B_TRUNCATE_BEGINNING

Cut from the beginning of the string until it fits within the specified width.

B_TRUNCATE_MIDDLE

Cut from the middle of the string.

B_TRUNCATE_END

Cut from the end of the string.

B_TRUNCATE_SMART

Cut anywhere, but do so intelligently, so that all the strings remain different after being cut. For example, if a set of similar path names are passed in the inputStringArray, this mode would attempt to cut from the identical parts of the path names and preserve the parts that are different. This mode also pays attention to word boundaries, separators, punctuation, and the like. However, it’s not implemented for the current release.

ClipToPicture(), ClipInverseToPicture()

void BView::ClipToPicture(BPicture *picture, BPoint where = B_ORIGIN, bool sync = true)

void BView::ClipInverseToPicture(BPicture *picture, BPoint where = B_ORIGIN, bool sync = true)

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()

ConstrainClippingRegion()

virtual void BView::ConstrainClippingRegion(BRegion *region)

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()

GetClippingRegion()

void BView::GetClippingRegion(BRegion *region) const

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()

Static Functions

Instantiate()

static BArchivable *BView::Instantiate(BMessage *archive)

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()

Scripting Support

Suite: “suite/vnd.Be-view”

Frame

The Frame property represents the frame rectangle of the view. The frame is passed as a BRect (B_RECT_TYPE).

Message

Specifiers

Description

B_GET_PROPERTY

B_DIRECT_SPECIFIER

Returns the view’s frame rectangle.

B_SET_PROPERTY

B_DIRECT_SPECIFIER

Sets the view’s frame rectangle.

Hidden

The “Hidden” property determines the visibility of the view. The messages are equivalent to manipulating the view with the IsHidden(), Hide(), and Show(). Note that this differs slightly from BWindow’s Hidden property, where multiple hides or shows are not nested.

Message

Specifiers

Description

B_GET_PROPERTY

B_DIRECT_SPECIFIER

Returns true if the view is hidden; false otherwise.

B_SET_PROPERTY

B_DIRECT_SPECIFIER

Hides or shows the view.

View

The “View” property represents the child views of the current view. For all messages except B_COUNT_PROPERTIES, the current specifier is popped off the specifier stack before the scripting message is passed to the target view. Views can be specified either by index (as found by ChildAt()), or name (as found by FindView()).

Message

Specifiers

Description

B_COUNT_PROPERTIES

B_DIRECT_SPECIFIER

Returns the number of of child views.

any

B_INDEX_SPECIFIER, B_REVERSE_INDEX_SPECIFIER, B_NAME_SPECIFIER

Directs the scripting message to the specified view.

Suite: “suite/vnd.Be-container-view”

Shelf

The “Shelf” property pops the current specifier off the specifier stack and then passes the scripting message to the shelf. If no shelf is present, an error is returned.

Message

Specifiers

Description

any

B_DIRECT_SPECIFIER

Directs the scripting message to the shelf.

Archived Fields

The Archive() function adds the following fields to its BMessage argument:

Field

Type code

Description

_frame

B_RECT_TYPE

The view’s frame rectangle.

_resize_mode

B_INT32_TYPE

Resizing mode.

_flags

B_INT32_TYPE

View flags.

_fname (array)

B_STRING_TYPE

Font family and style.

_fflt (array)

B_FLOAT_TYPE

Font size, shear, and rotation (-1 if default).

_color (array)

B_INT32_TYPE

High, low, and view colors.

_evmask (array)

B_INT32_TYPE

Event mask and options.

_dbuf

B_INT32_TYPE

Double buffering flag.

_origin

B_POINT_TYPE

Origin.

_psize

B_FLOAT_TYPE

Pen size.

_ploc

B_POINT_TYPE

Pen location.

_lmcapjoin (array)

B_INT16_TYPE

Line cap mode and join mode.

_lmmiter

B_FLOAT_TYPE

Line mode miter value.

_blend (array)

B_INT16_TYPE

Blending alpha and mode.

_dmod

B_INT32_TYPE

Drawing mode.

_views

B_MESSAGE_TYPE

Archived child views (deep copy only).

Some of these fields may not be present if the setting they represent isn’t used, or is the default value. For example, if the font’s family and style were not changed, the _fname field won’t be found in the archive.