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MESA_swap_frame_usage.spec
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Name
MESA_swap_frame_usage
Name Strings
GLX_MESA_swap_frame_usage
Contact
Ian Romanick, IBM, idr at us.ibm.com
Status
Deployed in DRI drivers post-XFree86 4.3.
Version
Date: 5/1/2003 Revision: 1.1
Number
???
Dependencies
GLX_SGI_swap_control affects the definition of this extension.
GLX_MESA_swap_control affects the definition of this extension.
GLX_OML_sync_control affects the definition of this extension.
Based on WGL_I3D_swap_frame_usage version 1.3.
Overview
This extension allows an application to determine what portion of the
swap period has elapsed since the last swap operation completed. The
"usage" value is a floating point value on the range [0,max] which is
calculated as follows:
td
percent = ----
tf
where td is the time measured from the last completed buffer swap (or
call to enable the statistic) to when the next buffer swap completes, tf
is the entire time for a frame which may be multiple screen refreshes
depending on the swap interval as set by the GLX_SGI_swap_control or
GLX_OML_sync_control extensions.
The value, percent, indicates the amount of time spent between the
completion of the two swaps. If the value is in the range [0,1], the
buffer swap occurred within the time period required to maintain a
constant frame rate. If the value is in the range (1,max], a constant
frame rate was not achieved. The value indicates the number of frames
required to draw.
This definition of "percent" differs slightly from
WGL_I3D_swap_frame_usage. In WGL_I3D_swap_frame_usage, the measurement
is taken from the completion of one swap to the issuance of the next.
This representation may not be as useful as measuring between
completions, as a significant amount of time may pass between the
issuance of a swap and the swap actually occurring.
There is also a mechanism to determine whether a frame swap was
missed.
New Procedures and Functions
int glXGetFrameUsageMESA(Display *dpy,
GLXDrawable drawable,
float *usage)
int glXBeginFrameTrackingMESA(Display *dpy,
GLXDrawable drawable)
int glXEndFrameTrackingMESA(Display *dpy,
GLXDrawable drawable)
int glXQueryFrameTrackingMESA(Display *dpy,
GLXDrawable drawable,
int64_t *swapCount,
int64_t *missedFrames,
float *lastMissedUsage)
New Tokens
None
Additions to Chapter 2 of the 1.4 GL Specification (OpenGL Operation)
None
Additions to Chapter 3 of the 1.4 GL Specification (Rasterization)
None
Additions to Chapter 4 of the 1.4 GL Specification (Per-Fragment Operations
and the Framebuffer)
None
Additions to Chapter 5 of the 1.4 GL Specification (Special Functions)
None
Additions to Chapter 6 of the 1.4 GL Specification (State and State Requests)
None
Additions to the GLX 1.3 Specification
The frame usage is measured as the percentage of the swap period elapsed
between two buffer-swap operations being committed. In unextended GLX the
swap period is the vertical refresh time. If SGI_swap_control or
MESA_swap_control are supported, the swap period is the vertical refresh
time multiplied by the swap interval (or one if the swap interval is set
to zero).
If OML_sync_control is supported, the swap period is the vertical
refresh time multiplied by the divisor parameter to
glXSwapBuffersMscOML. The frame usage in this case is less than 1.0 if
the swap is committed before target_msc, and is greater than or equal to
1.0 otherwise. The actual usage value is based on the divisor and is
never less than 0.0.
int glXBeginFrameTrackingMESA(Display *dpy,
GLXDrawable drawable,
float *usage)
glXGetFrameUsageMESA returns a floating-point value in <usage>
that represents the current swap usage, as defined above.
Missed frame swaps can be tracked by calling the following function:
int glXBeginFrameTrackingMESA(Display *dpy,
GLXDrawable drawable)
glXBeginFrameTrackingMESA resets a "missed frame" count and
synchronizes with the next frame vertical sync before it returns.
If a swap is missed based in the rate control specified by the
<interval> set by glXSwapIntervalSGI or the default swap of once
per frame, the missed frame count is incremented.
The current missed frame count and total number of swaps since
the last call to glXBeginFrameTrackingMESA can be obtained by
calling the following function:
int glXQueryFrameTrackingMESA(Display *dpy,
GLXDrawable drawable,
int64_t *swapCount,
int64_t *missedFrames,
float *lastMissedUsage)
The location pointed to by <swapCount> will be updated with the
number of swaps that have been committed. This value may not match the
number of swaps that have been requested since swaps may be
queued by the implementation. This function can be called at any
time and does not synchronize to vertical blank.
The location pointed to by <missedFrames> will contain the number
swaps that missed the specified frame. The frame usage for the
last missed frame is returned in the location pointed to by
<lastMissedUsage>.
Frame tracking is disabled by calling the function
int glXEndFrameTrackingMESA(Display *dpy,
GLXDrawable drawable)
This function will not return until all swaps have occurred. The
application can call glXQueryFrameTrackingMESA for a final swap and
missed frame count.
If these functions are successful, zero is returned. If the context
associated with dpy and drawable is not a direct context,
GLX_BAD_CONTEXT is returned.
Errors
If the function succeeds, zero is returned. If the function
fails, one of the following error codes is returned:
GLX_BAD_CONTEXT The current rendering context is not a direct
context.
GLX Protocol
None. This extension only extends to direct rendering contexts.
New State
None
New Implementation Dependent State
None
Revision History
1.1, 5/1/03 Added contact information.
1.0, 3/17/03 Initial version based on WGL_I3D_swap_frame_usage.