Extended Visual Information Extension

X Project Team Standard

Peter Daifuku

   Silicon Graphics, Inc.

   X Version 11, Release 7.7

   Version 1.0

   Copyright © 1986-1997 The Open Group

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     __________________________________________________________

   Table of Contents

   1. Introduction
   2. Goals
   3. Requests
   4. Events and Errors
   5. Changes to existing protocol.
   6. Encoding
   7. C Language Binding

Chapter 1. Introduction

   EVI (Extended Visual Information extension) allows a client to
   determine information about core X visuals beyond what the core
   protocol provides.

Chapter 2. Goals

   As the X Window System has evolved, it has become clear that
   the information returned by the core X protocol regarding
   Visuals is often insufficient for a client to determine which
   is the most appropriate visual for its needs. This extension
   allows clients to query the X server for additional visual
   information, specifically as regards colormaps and framebuffer
   levels.

   This extension is meant to address the needs of pure X clients
   only. It is specifically and purposefully not designed to
   address the needs of X extensions. Extensions that have an
   impact on visual information should provide their own
   mechanisms for delivering that information. For example, the
   Double Buffering Extension (DBE) provides its own mechanism for
   determining which visuals support double-buffering.

Chapter 3. Requests

   GetVersion
   client_major_version: CARD8
   client_minor_version: CARD8
   =>
   server_major_version: CARD8
   server_minor_version: CARD8

   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 EVI 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).

   GetVisualInfo
   visual_list: LISTofVISUALID
   =>
   per_visual_info: LISTofVISUALINFO

   where:
   VISUALINFO: [core_visual_id: VISUALID
   screen: CARD8
   level: INT8
   transparency_type: CARD8
   unused: CARD8
   transparency_value: CARD32
   min_hw_colormaps: CARD8
   max_hw_colormaps: CARD8
   num_colormap_conflicts: CARD16
   colormap_conflicts: LISTofVISUALID]
     * level is 0 for normal planes, > 0 for overlays, < 0 for
       underlays.
     * transparency_type is 0 for none, 1 for transparent pixel, 2
       for transparent mask.
     * transparency_value: value to get transparent pixel if
       transparency supported.
     * min_hw_colormaps: minimum number of hardware colormaps
       backing up the visual.
     * max_hw_colormaps: maximum number of hardware colormaps
       backing up the visual.
       (architectures with static colormap allocation/reallocation
       would have min = max)
     * num_colormap_conflicts: number of elements in
       colormap_conflicts.
     * colormap_conflicts: list of visuals that may conflict with
       this one. For example, if a 12-bit colormap is overloaded
       to support 8-bit visuals, the 8-bit visuals would conflict
       with the 12-bit visuals.

Chapter 4. Events and Errors

   No new events or errors are defined by this extension.

Chapter 5. Changes to existing protocol.

   None.

Chapter 6. Encoding

   The name of this extension is "Extended-Visual-Information".

   The conventions used here are the same as those for the core
   X11 Protocol Encoding.
GetVersion
     1     CARD8               opcode
     1     0                   EVI 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_version
     20                        unused

GetVisualInfo
     1     CARD8               opcode
     1     1                   EVI opcode
     2     2+n                 request length
     4     CARD32              n_visual
     4n    CARD32              visual_ids
=>
     1     1                   reply
     1                         unused
     2     CARD16              sequence number
     4     n                   length
     4     CARD32              n_info
     4     CARD32              n_conflicts
     16                        unused
     16n   LISTofVISUALINFO    items

VISUALINFO
     4     VisualID            core_visual_id
     1     INT8                screen
     1     INT8                level
     1     CARD8               transparency_type
     1     CARD8               unused
     4     CARD32              transparency_value
     1     CARD8               min_hw_colormaps
     1     CARD8               max_hw_colormaps
     2     CARD16              num_colormap_conflicts

Chapter 7. 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 Xevi 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/XEVI.h>.

   Bool XeviQueryVersion(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.

   XeviQueryVersion sets major_version_return and
   minor_version_return to the major and minor EVI protocol
   version supported by the server. If the EVI library is
   compatible with the version returned by the server, it returns
   nonzero. If dpy does not support the EVI 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 Xevi functions may be called before this
   function. If a client violates this rule, the effects of all
   subsequent Xevi calls that it makes are undefined.

   To get the extended information for any subset of visuals use
   XeviGetVisualInfo.

   int XeviGetVisualInfo(Display *display, VisualID *visual, int
   n_visual, ExtendedVisualInfo **evi_return, int *n_info_return);

   display

   Specifies the connection to the X server.

   visual

   If NULL, then information for all visuals of all screens is
   returned. Otherwise, a pointer to a list of visuals for which
   extended visual information is desired.

   n_visual

   If 0, then information for all visuals of all screens is
   returned. Otherwise, the number of elements in the array
   visual.

   evi_return

   Returns a pointer to a list of ExtendedVisualInfo. When done,
   the client should free the list using XFree.

   n_info_return

   Returns the number of elements in the list of
   ExtendedVisualInfo.

   XeviGetVisualInfo returns a list of ExtendedVisualInfo
   structures that describe visual information beyond that
   supported by the core protocol. This includes layer information
   relevant for systems supporting overlays and/or underlay
   planes, and information that allows applications better to
   determine the level of hardware support for multiple colormaps.
   XeviGetVisualInfo returns Success if successful, or an X error
   otherwise.
