Chip 2001 August - Disc 2/chip_20018102_hu.iso/linux/X-4.1.0/doc/tog-cup.txt

Text File | 2001-06-27 | 11KB | 595 lines

     Colormap Utilization Policy and Extension



            Version 1.0
          X Project Team Standard
         X Version 11, Release 6.4






             Kaleb S. KEITHLEY
               The Open Group









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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 col-
ormap 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 accomodate special col-
ormap 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 col-
ormap at the same locaton as in the default colormap
(instead of in the first available location.)

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_ver-
sion indicate what version of the protocol the client wants
the server to implement.  The server version numbers
returned indicate the protocol this extension actually sup-
ports. This might not equal the version sent by the client.
An implementation can (but need not) support more than one



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    X11 Colormap Utilization Policy and Extension


version simultaneously. The server_major_version and the
server_minor_version are a mechanism to support future revi-
sions of the TOG-CUP protocol that may be necessary. In gen-
eral, 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 applica-
tions 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 ele-
ments 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



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    X11 Colormap Utilization Policy and Extension


belong to a GrayScale, PseudoColor, or DirectColor visual.


3.  Events and Errors

No new events or errors are defined by this extension.


4.  Changes to existing protocol.

None.


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           LISTofCOLORITEMitems



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    X11 Colormap Utilization Policy and Extension


StoreColors
  1  CARD8         opcode
  1  2             TOG-CUP opcode
  2  2+3n         request length
  4  COLORMAP         cmap
  12n           LISTofCOLORITEMitems


 =>
  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 CUPStoreCol-
ors 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



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 proto-
col 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>.












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    X11 Colormap Utilization Policy and Extension

__
|
StatusXCupQueryVersion(
    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_ver-
sion_return to the major and minor TOG-CUP protocol version
supported by the server.  If the TOG-CUP library is compati-
ble 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 incompat-
ible, 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 XCupGetRe-
servedColormapEntries.

__
|
StatusXCupGetReservedColormapEntries(
    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 spe-
cific 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.



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To allocate one or more read-only color cells with RGB val-
ues, use XCupStoreColors.

__
|
StatusXCupStoreColors(
    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.


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 preallo-
cate Black and White pixels.  PC X servers should also pre-
allocate the MS-Windows desktop colors. (Note to implemen-
tors: in the Sample Implementation special colors are allo-
cated 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 col-
ormap 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 sharable (read-only) and any
other application which allocates the same color will share



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    X11 Colormap Utilization Policy and Extension


that color cell.
























































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