Colormap Utilization Policy and Extension
X Project Team Standard
Kaleb S. Keithley
The Open Group
X Version 11, Release 7.7
Version 1.0
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Table of Contents
1. Overview
2. Requests
3. Events and Errors
4. Changes to existing protocol.
5. Encoding
6. C Language Binding
7. Using the TOG-CUP extension and Colormap Utilization Policy
Chapter 1. Overview
This extension has three purposes: a) to provide mechanism for a special
application (a colormap manager) to discover any special colormap requirements,
e.g. the colormap entries that are nominally reserved for desktop colors in the
MS-Windows environment and initialize the default colormap so that it can be
more easily shared; and b) to encourage colormap sharing and reduce colormap
flashing on low-end 8-bit frame buffers by providing a policy for sharing; and
c) when colormaps aren't shared, define a behavior in the X server color
allocation scheme to reduce colormap flashing.
To encourage colormap sharing and accommodate special colormap requirements two
new protocols are defined: the first provides a way to query the server for a
list of reserved colormap entries, and the second is a way to initialize
read-only (shareable) colormap entries at specific locations in a colormap.
To minimize colormap flashing when the root window's default visual is one of
GrayScale, PseudoColor, or DirectColor, and a private colormap for the default
visual is being used, a minor (but compatible) change to the server
implementation of the AllocColor and AllocNamedColor requests is required.
Where the core protocol says nothing about the pixel values returned, when this
extension is in effect, the AllocColor and AllocNamedColor requests will first
look for a matching color in the default colormap, and, if a match is found and
the same cell in the private colormap has not already been allocated, the color
will be allocated in the private colormap at the same locaton as in the default
colormap (instead of in the first available location.)
Chapter 2. Requests
QueryVersion
client_major_version: CARD16
client_minor_version: CARD16
=>
server_major_version: CARD16
server_minor_version: CARD16
If supplied, the client_major_version and client_minor_version indicate what
version of the protocol the client wants the server to implement. The server
version numbers returned indicate the protocol this extension actually
supports. This might not equal the version sent by the client. An
implementation can (but need not) support more than one version simultaneously.
The server_major_version and the server_minor_version are a mechanism to
support future revisions of the TOG-CUP protocol that may be necessary. In
general, the major version would increment for incompatible changes, and the
minor version would increment for small upward-compatible changes. Servers that
support the protocol defined in this document will return a
server_major_version of one (1), and a server_minor_version of zero (0).
GetReservedColormapEntries
screen: CARD32
=>
entries: LISTofCOLORITEM
This request returns a list of colormap entries (pixels) that are reserved by
the system, e.g. MS-Windows reserved desktop colors. This list will, at a
minimum, contain entries for the BlackPixel and WhitePixel of the specified
screen. The do-red, do-green, and do-blue elements of the COLORITEMs are unused
in this reply.
Rationale: There are colormap entries (pixels) that, e.g., MS-Windows desktop
reserves as desktop colors, that should not be altered. If they are altered
then X programs will cause colormap flashing between X and MS-Windows
applications running/displaying on the same desktop.
StoreColors
cmap: COLORMAP
items: LISTofCOLORITEM
=>
items: LISTofCOLORITEM
This request changes the colormap entries of the specified pixels. The colormap
entries are allocated as if by an AllocColor request. The do-red, do-green, and
do-blue elements of the COLORITEMs are unused in this request. A boolean
alloc-ok element (a bit) is returned indicating whether the particular pixel
was successfully allocated or not. If successfully allocated the RGB and pixel
are returned.
A Value error is generated if a pixel is not a valid index into cmap. A
BadMatch error is generated if if cmap does not belong to a GrayScale,
PseudoColor, or DirectColor visual.
Chapter 3. Events and Errors
No new events or errors are defined by this extension.
Chapter 4. Changes to existing protocol.
None.
Chapter 5. Encoding
The name of this extension is "TOG-CUP".
The conventions used here are the same as those for the core X11 Protocol
Encoding.
QueryVersion
1 CARD8 opcode
1 0 TOG-CUP opcode
2 2 request length
2 CARD16 client_major_version
2 CARD16 client_minor_version
=>
1 1 reply
1 unused
2 CARD16 sequence number
4 0 length
2 CARD16 server_major_version
2 CARD16 server_minor_number
20 unused
GetReservedColormapEntries
1 CARD8 opcode
1 1 TOG-CUP opcode
2 2 request length
4 CARD32 screen
=>
1 1 reply
1 unused
2 CARD16 sequence number
4 3n length
24 unused
12n LISTofCOLORITEM items
StoreColors
1 CARD8 opcode
1 2 TOG-CUP opcode
2 2+3n request length
4 COLORMAP cmap
12n LISTofCOLORITEM items
=>
1 1 reply
1 unused
2 CARD16 sequence number
4 3n length
24 unused
12n LISTofCOLORITEM items
(The definition of COLORITEM here is only for the purpose of defining the
additional alloc-ok member in the CUPStoreColors reply.)
COLORITEM
4 CARD32 pixel
2 CARD16 red
2 CARD16 green
2 CARD16 blue
1 alloc-ok
#x07 unused
#x08 alloc-ok (1 is True, 0 is False)
#xF0 unused
1 unused
Chapter 6. C Language Binding
The C functions provide direct access to the protocol and add no additional
semantics. For complete details on the effects of these functions, refer to the
appropriate protocol request, which can be derived by deleting XCup at the
start of the function. All functions that have return type Status will return
nonzero for success and zero for failure.
The include file for this extension is <X11/extensions/Xcup.h>.
Status XCupQueryVersion(Display* display, int* major_version_return, int*
minor_version_return);
display Specifies the connection to the X server.
major_version_return Returns the major version supported by the server.
minor_version_return Returns the minor version supported by the server.
XCupQueryVersions sets major_version_return and minor_version_return to the
major and minor TOG-CUP protocol version supported by the server. If the
TOG-CUP library is compatible with the version returned by the server, it
returns nonzero. If dpy does not support the TOG-CUP extension, or if there was
an error during communication with the server, or if the server and library
protocol versions are incompatible, it returns zero. No other XCup functions
may be called before this function. If a client violates this rule, the effects
of all subsequent XCup calls that it makes are undefined.
To get the list of reserved colormap entries, use
XCupGetReservedColormapEntries.
Status XCupGetReservedColormapEntries(Display* display, int screen, XColor**
colors_out, int* ncolors);
display Specifies the connection to the X server.
colors_out Returns the values reserved by the server.
ncolors Returns the number of items in colors_out.
The XCupGetReservedColormapEntries function gets system specific colormap
entries. E.g. the MS-Windows desktop uses N colormap entries at the beginning
(0..N) and end (256-N..255) of the colormap. Use XFree to free colors_out.
To allocate one or more read-only color cells with RGB values, use
XCupStoreColors.
Status XCupStoreColors(Display* display, Colormap colormap, XColor*
colors_in_out, int ncolors);
display Specifies the connection to the X server.
colormap Specifies the colormap.
colors_in_out Specifies and returns the values actually used in the colormap.
ncolors Specifies the number of items in colors_in_out.
The XCupStoreColors function changes the colormap entries of the pixel values
specified in the pixel members of the XColor structures. The colormap entries
are allocated as if an AllocColor had been used instead, i.e. the colors are
read-only (shareable). XCupStoreColors returns the number of colors that were
successfully allocated in the colormap.
Chapter 7. Using the TOG-CUP extension and Colormap Utilization Policy
The X server preallocates any hardware or desktop special colors in the default
colormap; e.g. UNIX X servers preallocate Black and White pixels. PC X servers
should also preallocate the MS-Windows desktop colors. (Note to implementors:
in the Sample Implementation special colors are allocated in the default
colormap in cfbCreateDefColormap for dumb memory framebuffers.)
To minimize colormap flash an application which installs its own private
colormap should query the special colors by calling
XCupGetReservedColormapEntries, and can then store those entries (in the proper
location) in its private colormap using XCupStoreColors.
Applications which allocate many colors in a screen's default colormap, e.g. a
color-cube or a gray-ramp, should allocate them with XCupStoreColors. By using
XCupStoreColors the colors will be allocated shareable (read-only) and any
other application which allocates the same color will share that color cell.
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