X Nonrectangular Window Shape Extension Library

X Consortium Standard

Keith Packard

   MIT X Consortium

   X Version 11, Release 7.7

   Version 1.0

   Copyright © 1989 X Consortium

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     __________________________________________________________

   Table of Contents

   1. Overview
   2. Description
   3. C Language Binding
   Glossary

Chapter 1. Overview

   This extension provides arbitrary window and border shapes
   within the X11 protocol.

   The restriction of rectangular windows within the X protocol is
   a significant limitation in the implementation of many styles
   of user interface. For example, many transient windows would
   like to display a "drop shadow" to give the illusion of 3
   dimensions. As another example, some user interface style
   guides call for buttons with rounded corners; the full
   simulation of a nonrectangular shape, particularly with respect
   to event distribution and cursor shape, is not possible within
   the core X protocol. As a final example, round clocks and
   nonrectangular icons are desirable visual addition to the
   desktop.

   This extension provides mechanisms for changing the visible
   shape of a window to an arbitrary, possibly disjoint,
   nonrectangular form. The intent of the extension is to
   supplement the existing semantics, not replace them. In
   particular, it is desirable for clients that are unaware of the
   extension to still be able to cope reasonably with shaped
   windows. For example, window managers should still be able to
   negotiate screen real estate in rectangular pieces. Toward this
   end, any shape specified for a window is clipped by the
   bounding rectangle for the window as specified by the window's
   geometry in the core protocol. An expected convention would be
   that client programs expand their shape to fill the area
   offered by the window manager.

Chapter 2. Description

   Each window (even with no shapes specified) is defined by two
   regions: the bounding region and the clip region. The bounding
   region is the area of the parent window that the window will
   occupy (including border). The clip region is the subset of the
   bounding region that is available for subwindows and graphics.
   The area between the bounding region and the clip region is
   defined to be the border of the window.

   A nonshaped window will have a bounding region that is a
   rectangle spanning the window, including its border; the clip
   region will be a rectangle filling the inside dimensions (not
   including the border). In this document, these areas are
   referred to as the default bounding region and the default clip
   region. For a window with inside size of width by height and
   border width bwidth, the default bounding and clip regions are
   the rectangles (relative to the window origin):

   bounding.x = -bwidth
   bounding.y = -bwidth
   bounding.width = width + 2 * bwidth
   bounding.height = height + 2 * bwidth
   clip.x = 0
   clip.y = 0
   clip.width = width
   clip.height = height

   This extension allows a client to modify either or both of the
   bounding or clip regions by specifying new regions that combine
   with the default regions. These new regions are called the
   client bounding region and the client clip region. They are
   specified relative to the origin of the window and are always
   defined by offsets relative to the window origin (that is,
   region adjustments are not required when the window is moved).
   Three mechanisms for specifying regions are provided: a list of
   rectangles, a bitmap, and an existing bounding or clip region
   from a window. This is modeled on the specification of regions
   in graphics contexts in the core protocol and allows a variety
   of different uses of the extension.

   When using an existing window shape as an operand in specifying
   a new shape, the client region is used, unless none has been
   set, in which case the default region is used instead.

   The effective bounding region of a window is defined to be the
   intersection of the client bounding region with the default
   bounding region. Any portion of the client bounding region that
   is not included in the default bounding region will not be
   included in the effective bounding region on the screen. This
   means that window managers (or other geometry managers) used to
   dealing with rectangular client windows will be able to
   constrain the client to a rectangular area of the screen.

   Construction of the effective bounding region is dynamic; the
   client bounding region is not mutated to obtain the effective
   bounding region. If a client bounding region is specified that
   extends beyond the current default bounding region, and the
   window is later enlarged, the effective bounding region will be
   enlarged to include more of the client bounding region.

   The effective clip region of a window is defined to be the
   intersection of the client clip region with both the default
   clip region and the client bounding region. Any portion of the
   client clip region that is not included in both the default
   clip region and the client bounding region will not be included
   in the effective clip region on the screen.

   Construction of the effective clip region is dynamic; the
   client clip region is not mutated to obtain the effective clip
   region. If a client clip region is specified that extends
   beyond the current default clip region and the window or its
   bounding region is later enlarged, the effective clip region
   will be enlarged to include more of the client clip region if
   it is included in the effective bounding region.

   The border of a window is defined to be the difference between
   the effective bounding region and the effective clip region. If
   this region is empty, no border is displayed. If this region is
   nonempty, the border is filled using the border-tile or
   border-pixel of the window as specified in the core protocol.
   Note that a window with a nonzero border width will never be
   able to draw beyond the default clip region of the window. Also
   note that a zero border width does not prevent a window from
   having a border, since the clip shape can still be made smaller
   than the bounding shape.

   All output to the window and visible regions of any subwindows
   will be clipped to the effective clip region. The server must
   not retain window contents beyond the effective bounding region
   with backing store. The window's origin (for graphics
   operations, background tiling, and subwindow placement) is not
   affected by the existence of a bounding region or clip region.

   Areas that are inside the default bounding region but outside
   the effective bounding region are not part of the window; these
   areas of the screen will be occupied by other windows. Input
   events that occur within the default bounding region but
   outside the effective bounding region will be delivered as if
   the window was not occluding the event position. Events that
   occur in a nonrectangular border of a window will be delivered
   to that window, just as for events that occur in a normal
   rectangular border.

   An InputOnly window can have its bounding region set, but it is
   a Match error to attempt to set a clip region on an InputOnly
   window or to specify its clip region as a source to a request
   in this extension.

   The server must accept changes to the clip region of a root
   window, but the server is permitted to ignore requested changes
   to the bounding region of a root window. If the server accepts
   bounding region changes, the contents of the screen outside the
   bounding region are implementation dependent.

Chapter 3. C Language Binding

   The C functions provide direct access to the protocol and add
   no additional semantics.

   The include file for this extension is
   <X11/extensions/shape.h>. The defined shape kinds are
   ShapeBounding and ShapeClip The defined region operations are
   ShapeSet ShapeUnion ShapeIntersect ShapeSubtract and
   ShapeInvert.

   Bool XShapeQueryExtension(Display *display, int *event_base,
   int *error_base);

   XShapeQueryExtension returns True if the specified display
   supports the SHAPE extension else False If the extension is
   supported, *event_base is set to the event number for
   ShapeNotify events and *error_base would be set to the error
   number for the first error for this extension. Because no
   errors are defined for this version of the extension, the value
   returned here is not defined (nor useful).

   Status XShapeQueryVersion(Display *display, int *major_version,
   int *minor_version);

   If the extension is supported, XShapeQueryVersion sets the
   major and minor version numbers of the extension supported by
   the display and returns a nonzero value. Otherwise, the
   arguments are not set and zero is returned.

   XShapeCombineRegion(Display *display, Window dest, int
   dest_kind, int x_off, int y_off, int region, int op, REGION
   *region);

   XShapeCombineRegion converts the specified region into a list
   of rectangles and calls XShapeCombineRectangles

   XShapeCombineRectangles(Display *display, Window dest, int
   dest_kind, int x_off, int y_off, XRectangle *rectangles, int
   n_rects, int op, int ordering);

   If the extension is supported, XShapeCombineRectangles performs
   a ShapeRectangles operation; otherwise, the request is ignored.

   XShapeCombineMask(Display *display, int dest, int dest_kind,
   int x_off, int y_off, Pixmap src, int op);

   If the extension is supported, XShapeCombineMask performs a
   ShapeMask operation; otherwise, the request is ignored.

   XShapeCombineShape(Display *display, Window dest, int
   dest_kind, int x_off, int y_off, Window src, int src_kind, int
   op);

   If the extension is supported, XShapeCombineShape performs a
   ShapeCombine operation; otherwise, the request is ignored.

   XShapeOffsetShape(display, dest, dest_kind, x_off, y_off);

   If the extension is supported, XShapeOffsetShape performs a
   ShapeOffset operation; otherwise, the request is ignored.

   Status XShapeQueryExtents(Display *display, Window window, Bool
   *bounding_shaped, int *x_bounding, int *y_bounding, unsigned
   int *w_bounding, unsigned int *h_bounding, Bool *clip_shaped,
   int *x_clip, int *y_clip, unsigned int *w_clip, unsigned int
   *h_clip);

   If the extension is supported, XShapeQueryExtents sets
   x_bounding, y_bounding, w_bounding, h_bounding to the extents
   of the bounding shape and sets x_clip, y_clip, w_clip, h_clip
   to the extents of the clip shape. For unspecified client
   regions, the extents of the corresponding default region are
   used.

   If the extension is supported, a nonzero value is returned;
   otherwise, zero is returned.

   XShapeSelectInput(Display *display, Window window, unsigned
   long mask);

   To make this extension more compatible with other interfaces,
   although only one event type can be selected via the extension,
   XShapeSelectInput provides a general mechanism similar to the
   standard Xlib binding for window events. A mask value has been
   defined, ShapeNotifyMask that is the only valid bit in mask
   that may be specified. The structure for this event is defined
   as follows:

   typedef struct {
       int type;     /* of event */
       unsigned long serial;     /* # of last request processed by
    server */
       Bool send_event;     /* true if this came frome a SendEvent
    request */
       Display *display;     /* Display the event was read from */
       Window window;     /* window of event */
       int kind;     /* ShapeBounding or ShapeClip */
       int x, y;     /* extents of new region */
       unsigned width, height;
       Time time;     /* server timestamp when region changed */
       Bool shaped;     /* true if the region exists */
   } XShapeEvent;

   unsigned long XShapeInputSelected(Display *display, Window
   window);

   XShapeInputSelected returns the current input mask for
   extension events on the specified window; the value returned if
   ShapeNotify is selected for is ShapeNotifyMask otherwise, it
   returns zero. If the extension is not supported, it returns
   zero.

   XRectangle *XShapeGetRectangles(Display *display, Window
   window, int kind, int *count, int *ordering);

   If the extension is not supported, XShapeGetRectangles returns
   NULL. Otherwise, it returns a list of rectangles that describe
   the region specified by kind.

Glossary

   bounding region
          The area of the parent window that this window will
          occupy. This area is divided into two parts: the border
          and the interior.

   clip region
          The interior of the window, as a subset of the bounding
          region. This region describes the area that will be
          painted with the window background when the window is
          cleared, will contain all graphics output to the window,
          and will clip any subwindows.

   default bounding region
          The rectangular area, as described by the core protocol
          window size, that covers the interior of the window and
          its border.

   default clip region
          The rectangular area, as described by the core protocol
          window size, that covers the interior of the window and
          excludes the border.

   client bounding region
          The region associated with a window that is directly
          modified via this extension when specified by
          ShapeBounding This region is used in conjunction with
          the default bounding region to produce the effective
          bounding region.

   client clip region
          The region associated with a window that is directly
          modified via this extension when specified by ShapeClip
          This region is used in conjunction with the default clip
          region and the client bounding region to produce the
          effective clip region.

   effective bounding region
          The actual shape of the window on the screen, including
          border and interior (but excluding the effects of
          overlapping windows). When a window has a client
          bounding region, the effective bounding region is the
          intersection of the default bounding region and the
          client bounding region. Otherwise, the effective
          bounding region is the same as the default bounding
          region.

   effective clip region
          The actual shape of the interior of the window on the
          screen (excluding the effects of overlapping windows).
          When a window has a client clip region or a client
          bounding region, the effective clip region is the
          intersection of the default clip region, the client clip
          region (if any) and the client bounding region (if any).
          Otherwise, the effective clip region is the same as the
          default clip region.
