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.

              If NULL, then information for all visuals of all screens is
visual        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.

