














		  X Nonrectangular Window

		  Shape Extension Library



			Version 1.0
		   X Consortium Standard
		 X Version 11, Release 6.7






		       Keith Packard
		      MIT X Consortium









Copyright (C) 1989 X Consortium

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without prior written authorization from the X Consortium.

























































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 win-
dows 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 cor-
ners; the full simulation of a nonrectangular shape, partic-
ularly 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, non-
rectangular form.  The intent of the extension is to supple-
ment the existing semantics, not replace them.	In particu-
lar, 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 conven-
tion would be that client programs expand their shape to
fill the area offered by the window manager.

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 sub-
windows and graphics.  The area between the bounding region
and the clip region is defined to be the border of the win-
dow.

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 dimen-
sions (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 ori-
gin):






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       X Nonrectangular Window Shape Extension Library

__
|
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 speci-
fying 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



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       X Nonrectangular Window Shape Extension Library


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 win-
dow 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 subwin-
dows 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 out-
side the effective bounding region are not part of the win-
dow; these areas of the screen will be occupied by other
windows.  Input events that occur within the default bound-
ing region but outside the effective bounding region will be
delivered as if the window was not occluding the event posi-
tion.  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 Inpu-
tOnly 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 depen-
dent.




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       X Nonrectangular Window Shape Extension Library


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/exten-
sions/shape.h>.  The defined shape kinds are ShapeBounding
and ShapeClip.	The defined region operations are ShapeSet,
ShapeUnion, ShapeIntersect, ShapeSubtract, and ShapeInvert.
__
|
Bool
XShapeQueryExtension(display, event_base, error_base)
     Display *display;
     int *event_base; /* RETURN */
     int *error_base; /* RETURN */

|__

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).


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

|__

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.


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

|__

XShapeCombineRegion converts the specified region into a



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       X Nonrectangular Window Shape Extension Library


list of rectangles and calls XShapeCombineRectangles.


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

|__

If the extension is supported, XShapeCombineRectangles per-
forms a ShapeRectangles operation; otherwise, the request is
ignored.


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

|__

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


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

|__

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














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       X Nonrectangular Window Shape Extension Library

__
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XShapeOffsetShape(display, dest, dest_kind, x_off, y_off)
      Display *display;
      Window dest;
      int dest_kind, fIx_off, y_off;

|__

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


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

|__

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.


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

|__

To make this extension more compatible with other inter-
faces, 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:






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       X Nonrectangular Window Shape Extension Library

__
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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;

|__


__
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unsigned long
XShapeInputSelected(display, window)
     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; other-
wise, it returns zero.	If the extension is not supported,
it returns zero.


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

|__

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

4.  Glossary







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       X Nonrectangular Window Shape Extension Library


bounding region

     The area of the parent window that this window will
     occupy.  This area is divided into two parts:  the bor-
     der 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 win-
     dow, 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 Shape-
     Bounding.	This region is used in conjunction with the
     default bounding region to produce the effective bound-
     ing 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 over-
     lapping windows).	When a window has a client bounding
     region, the effective bounding region is the intersec-
     tion of the default bounding region and the client
     bounding region.  Otherwise, the effective bounding
     region is the same as the default bounding region.






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       X Nonrectangular Window Shape Extension Library


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.















































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