X Nonrectangular Window Shape Extension Protocol

X.Org Standard

Keith Packard

MIT X Consortium
Intel Corporation

Hideki Hiura

SunSoft, Inc.

X Version 11, Release 7.7

Version 1.1

Copyright © 1989, 2004 The Open Group

Copyright © 2006 Keith Packard

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Table of Contents

1. Overview
2. Description
3. Types
4. Requests
5. Events
6. Encoding
    New Types
    Requests
    Events
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 both the visible and
interactive shape of a window to arbitrary, possibly disjoint, nonrectangular
forms. 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 three regions: the 
bounding region, the clip region and the input 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. The input region is the
subset of the bounding region that can "contain" the pointer.

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); the input region will match the
bounding region. In this document, these areas are referred to as the default
bounding region, the default clip region and the default input region. For a
window with inside size of width by height and border width bwidth, the default
bounding, clip and input 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

input.x = -bwidth
input.y = -bwidth
input.width = width + 2 * bwidth
input.height = height + 2 * bwidth

This extension allows a client to modify any combination of the bounding, clip
or input regions by specifying new regions that combine with the default
regions. These new regions are called the client bounding region, the client
clip region and the client input 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.

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

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

The following types are used in the request and event definitions in subsequent
sections.

SHAPE_KIND: { Bounding, Clip, Input }

SHAPE_OP: { Set, Union, Intersect, Subtract, Invert }

Set indicates that the region specified as an explicit source in the request is
stored unaltered as the new destination client region. Union indicates that the
source and destination regions are unioned together to produce the new
destination client region. Intersect indicates that the source and destination
regions are intersected together to produce the new destination client region.
Subtract indicates that the source region is subtracted from the destination
region to produce the new destination region. Invert indicates that the
destination region is subtracted from the source region to produce the new
destination region.

Chapter 4. Requests

ShapeQueryVersion

=>

majorVersion: CARD16

minorVersion: CARD16

This request can be used to ensure that the server version of the SHAPE
extension is usable by the client. This document defines major version one (1),
minor version one (1).

ShapeRectangles

dest: WINDOW
destKind: SHAPE_KIND
op: SHAPE_OP
xOff, yOff: INT16
rectangles: LISTofRECTANGLES
ordering: { UnSorted, YSorted, YXSorted, YXBanded }
Errors: Window, Length, Match, Value

This request specifies an array of rectangles, relative to the origin of the
window plus the specified offset (xOff and yOff) that together define a region.
This region is combined (as specified by the operator op) with the existing
client region (specified by destKind) of the destination window, and the result
is stored as the specified client region of the destination window. Note that
the list of rectangles can be empty, specifying an empty region; this is not
the same as passing None to ShapeMask,

If known by the client, ordering relations on the rectangles can be specified
with the ordering argument. This may provide faster operation by the server.
The meanings of the ordering values are the same as in the core protocol
SetClipRectangles request. If an incorrect ordering is specified, the server
may generate a Match error, but it is not required to do so. If no error is
generated, the graphics results are undefined. Except for UnSorted , the
rectangles should be nonintersecting, or the resulting region will be
undefined. UnSorted means that the rectangles are in arbitrary order. YSorted
means that the rectangles are nondecreasing in their Y origin. YXSorted
additionally constrains YSorted order in that all rectangles with an equal Y
origin are nondecreasing in their X origin. YXBanded additionally constrains
YXSorted by requiring that, for every possible Y scanline, all rectangles that
include that scanline have identical Y origins and Y extents.

ShapeMask

dest: WINDOW destKind: SHAPE_KIND op: SHAPE_OP xOff, yOff: INT16 source: PIXMAP
or None
Errors: Window, Pixmap, Match, Value

The source in this request is a 1-bit deep pixmap, or None . If source is None
, the specified client region is removed from the window, causing the effective
region to revert to the default region. The ShapeNotify event generated by this
request and subsequent ShapeQueryExtents will report that a client shape has
not been specified. If a valid pixmap is specified, it is converted to a
region, with bits set to one included in the region and bits set to zero
excluded, and an offset from the window origin as specified by xOff and yOff.
The resulting region is then combined (as specified by the operator op) with
the existing client region (indicated by destKind) of the destination window,
and the result is stored as the specified client region of the destination
window. The source pixmap and destination window must have been created on the
same screen, or else a Match error results.

ShapeCombine

dest: WINDOW
destKind: SHAPE_KIND
op: SHAPE_OP
xOff, yOff: INT16
source: WINDOW
sourceKind: SHAPE_KIND
Errors: Window, Match, Value

The client region, indicated by sourceKind, of the source window is offset from
the window origin by xOff and yOff and combined with the client region,
indicated by destKind, of the destination window. The result is stored as the
specified client region of the destination window. The source and destination
windows must be on the same screen, or else a Match error results.

ShapeOffset

dest: WINDOW
destKind: SHAPE_KIND
xOff, yOff: INT16
Errors: Window, Match, Value

The client region, indicated by destKind, is moved relative to its current
position by the amounts xOff and yOff.

ShapeQueryExtents

dest: WINDOW

=>

boundingShaped: BOOL
clipShaped: BOOL
xBoundingShape: INT16
yBoundingShape: INT16
widthBoundingShape: CARD16
heightBoundingShape: CARD16
xClipShape: INT16
yClipShape: INT16
widthClipShape: CARD16
heightClipShape: CARD16
Errors: Window

The boundingShaped and clipShaped results are True if the corresponding client
regions have been specified, else they are False . The x, y, width, and height
values define the extents of the client regions, when a client region has not
been specified, the extents of the corresponding default region are reported.

ShapeSelectInput

window: WINDOW
enable: BOOL
Errors: Window, Value

Specifying enable as True causes the server to send the requesting client a
ShapeNotify event whenever the bounding, clip or input region of the specified
window is altered by any client. Specifying enable as False causes the server
to stop sending such events.

ShapeInputSelected

window: WINDOW
=> enable: BOOL
Errors: Window

If enable is True, then ShapeNotify events for the window are generated for
this client.

ShapeGetRectangles

window: WINDOW
kind: SHAPE_KIND
=> rectangles: LISTofRECTANGLE
ordering: { UnSorted, YSorted, YXSorted, YXBanded }
Errors: Window, Match

A list of rectangles describing the region indicated by kind, and the ordering
of those rectangles, is returned. The meaning of the ordering values is the
same as in the ShapeRectangles request.

Chapter 5. Events

ShapeNotify

window: WINDOW
kind: SHAPE_KIND
shaped: BOOL
x, y: INT16
width, height: CARD16
time: TIMESTAMP

Whenever the client bounding, clip or input shape of a window is modified, a
ShapeNotify event is sent to each client that has used ShapeSelectInput to
request it.

Kind indicates which client region (bounding or clip) has been modified; shaped
is True when the window has a client shape of type kind, and is False when the
window no longer has a client shape of this type. The x, y, width, and height
indicate the extents of the current shape. When shaped is False these will
indicate the extents of the default region. The timestamp indicates the server
time when the shape was changed.

Chapter 6. Encoding

Table of Contents

New Types
Requests
Events

Please refer to the X11 Protocol Encoding document as this document uses
conventions established there.

The name of this extension is "SHAPE".

New Types

SHAPE_KIND
     0     Bounding
     1     Clip
     2     Input

SHAPE_OP
     0     Set
     1     Union
     2     Intersect
     3     Subtract
     4     Invert

Requests

ShapeQueryVersion
     1     CARD8              opcode
     1     0                  shape opcode
     2     1                  request length

=>
     1     1                  Reply
     1                        unused
     2     CARD16             sequence number
     4     0                  length
     2     CARD16             major version
     2     CARD16             minor version
     20                       unused

ShapeRectangles
     1     CARD8              opcode
     1     1                  shape opcode
     2     4+2n               request length
     1     SHAPE_OP           operation
     1     SHAPE_KIND         destination kind
     1                        ordering
           0     UnSorted
           1     YSorted
           2     YXSorted
           3     YXBanded
     1                        unused
     4     WINDOW             destination window
     2     INT16              x offset
     2     INT16              y offset
     8n    LISTofRECTANGLE    rectangles

ShapeMask
     1     CARD8              opcode
     1     2                  shape opcode
     2     5                  request length
     1     SHAPE_OP           operation
     1     SHAPE_KIND         destination kind
     2                        unused
     4     WINDOW             destination window
     2     INT16              x offset
     2     INT16              y offset
     4     PIXMAP             source bitmap
           0     None

ShapeCombine
     1     CARD8              opcode
     1     3                  shape opcode
     2     5                  request length
     1     SHAPE_OP           operation
     1     SHAPE_KIND         destination kind
     1     SHAPE_KIND         source kind
     1                        unused
     4     WINDOW             destination window
     2     INT16              x offset
     2     INT16              y offset
     4     WINDOW             source window

ShapeOffset
     1     CARD8              opcode
     1     4                  shape opcode
     2     4                  request length
     1     SHAPE_KIND         destination kind
     3                        unused
     4     WINDOW             destination window
     2     INT16              x offset
     2     INT16              y offset

ShapeQueryExtents
     1     CARD8              opcode
     1     5                  shape opcode
     2     2                  request length
     4     WINDOW             destination window

 =>
     1     1                  Reply
     1                        unused
     2     CARD16             sequence number
     4     0                  reply length
     1     BOOL               bounding shaped
     1     BOOL               clip shaped
     2                        unused
     2     INT16              bounding shape extents x
     2     INT16              bounding shape extents y
     2     CARD16             bounding shape extents width
     2     CARD16             bounding shape extents height
     2     INT16              clip shape extents x
     2     INT16              clip shape extents y
     2     CARD16             clip shape extents width
     2     CARD16             clip shape extents height
     4                        unused

ShapeSelectInput
     1     CARD8              opcode
     1     6                  shape opcode
     2     3                  request length
     4     WINDOW             destination window
     1     BOOL               enable
     3                        unused

ShapeInputSelected
     1     CARD8              opcode
     1     7                  shape opcode
     2     2                  request length
     4     WINDOW             destination window
 =>
     1     1                  Reply
     1     BOOL               enabled
     2     CARD16             sequence number
     4     0                  reply length
     24                       unused

ShapeGetRectangles
     1     CARD8              opcode
     1     8                  shape opcode
     2     3                  request length
     4     WINDOW             window
     1     SHAPE_KIND         source kind
     3                        unused
 =>
     1     1                  Reply
     1                        ordering
           0     UnSorted
           1     YSorted
           2     YXSorted
           3     YXBanded
     2     CARD16             sequence number
     4     2n                 reply length
     4     CARD32             nrects
     20                       unused
     8n    LISTofRECTANGLE    rectangles

Events

ShapeNotify
     1     CARD8               type (0 + extension event base)
     1     SHAPE_KIND          shape kind
     2     CARD16              sequence number
     4     WINDOW              affected window
     2     INT16               x value of extents
     2     INT16               y value of extents
     2     CARD16              width of extents
     2     CARD16              height of extents
     4     TIMESTAMP           server time
     1     BOOL                shaped
     11                        unused

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.

input region

    The subset of the bounding region which can ``contain'' the pointer.

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.

default input region

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

client input region

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

effective input region

    The actual shape of the window on the screen (excluding the effects of
    overlapping windows) which can ``contain'' the pointer. When a window has a
    client input region or a client bounding region, the effective input region
    is the intersection of the default input region, the client input region
    (if any) and the client bounding region (if any). Otherwise, the effective
    input region is the same as the default input region.

