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$Date: 1995/09/15 01:22:58 $ $Revision: 1.8 $
This extension provides a means for synchronization with the video
frame rate of a monitor. (In the case of an interlaced monitor,
this is typically the rate of displaying both the even and odd
fields of a frame.) The kernel maintains a video sync counter for
each physical hardware pipe in a system; the counter is incremented
upon the completion of the display of each full frame of video data. An
OpenGL context always corresponds to a pipe. When an OpenGL process
has a current context, it can put itself to sleep until the counter of
that pipe reaches a desired value. The process can also query the
value of the counter.
The counter runs as long as the graphics subsystem is running; it is
initialized via the /usr/gfx/gfxinit command. However, a process can
query or sleep on the counter only when a direct context is current.
Each of the procedures described below will fail and return an error
code if the current context is not a direct one.
The counter is an unsigned 32-bit integer.
Should glXWaitVideoSyncSGI return GLX_BAD_VALUE if <remainder> is
greater than or equal to <divisor>? (No.)
New Procedures and Functions
int glXGetVideoSyncSGI(uint *count);
int glXWaitVideoSyncSGI(int divisor,
int remainder,
unsigned int *count);
New Tokens
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and
the Framebuffer)
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
Additions to the GLX Specification
[Add to Section 3.2.5 of the 1.0 GLX Specification (Synchronization
In addition to its current functions, /usr/gfx/gfxinit also initializes
the video sync counter to zero. After that time the video sync counter
is incremented by one at the completion of the display of each full
frame of video data. The counter value wraps to zero after it reaches
its maximum value. The single video sync counter is shared by all
glXGetVideoSyncSGI returns the value of the video sync counter in
<count>. Zero is returned if the call is successful.
glXWaitVideoSyncSGI puts the calling process to sleep until
(C mod D) = R
where C is the video sync counter, D is specified by the <divisor>
parameter of glXWaitVideoSyncSGI, and R is specified by the <remainder>
parameter of glXWaitVideoSyncSGI. glXWaitVideoSyncSGI returns the
current video sync counter value in <count>. Zero is returned by
glXWaitVideoSyncSGI if it is successful.
glXWaitVideoSyncSGI is supported only by direct GLXContexts.
glXGetVideoSyncSGI returns GLX_BAD_CONTEXT if there is no current
glXWaitVideoSyncSGI returns GLX_BAD_CONTEXT if the current context is
not direct, or if there is no current context.
glXWaitVideoSyncSGI returns GLX_BAD_VALUE if parameter <divisor> is less
than or equal to zero, or if parameter <remainder> is less than zero.
New State
Get Value Get Command Type Initial Value
--------- ----------- ---- -------------
[video sync counter] glXGetVideoSyncSGI Z+ unknown
New Implementation Dependent State