X Nonrectangular Window Shape Extension Library

X Consortium Standard

Keith Packard

MIT X Consortium

X Version 11, Release 7.7

Version 1.0

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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 from 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.

