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    1 Name
    2 
    3     MESA_swap_frame_usage
    4 
    5 Name Strings
    6 
    7     GLX_MESA_swap_frame_usage
    8 
    9 Contact
   10 
   11     Ian Romanick, IBM, idr at us.ibm.com
   12 
   13 Status
   14 
   15     Deployed in DRI drivers post-XFree86 4.3.
   16 
   17 Version
   18 
   19     Date: 5/1/2003   Revision: 1.1
   20 
   21 Number
   22 
   23     ???
   24 
   25 Dependencies
   26 
   27     GLX_SGI_swap_control affects the definition of this extension.
   28     GLX_MESA_swap_control affects the definition of this extension.
   29     GLX_OML_sync_control affects the definition of this extension.
   30 
   31     Based on WGL_I3D_swap_frame_usage version 1.3.
   32 
   33 Overview
   34 
   35     This extension allows an application to determine what portion of the
   36     swap period has elapsed since the last swap operation completed.  The
   37     "usage" value is a floating point value on the range [0,max] which is
   38     calculated as follows:
   39 
   40                               td
   41                    percent = ----
   42                               tf
   43 
   44     where td is the time measured from the last completed buffer swap (or
   45     call to enable the statistic) to when the next buffer swap completes, tf
   46     is the entire time for a frame which may be multiple screen refreshes
   47     depending on the swap interval as set by the GLX_SGI_swap_control or
   48     GLX_OML_sync_control extensions. 
   49 
   50     The value, percent, indicates the amount of time spent between the
   51     completion of the two swaps.  If the value is in the range [0,1], the
   52     buffer swap occurred within the time period required to maintain a
   53     constant frame rate.  If the value is in the range (1,max], a constant
   54     frame rate was not achieved.  The value indicates the number of frames
   55     required to draw.
   56 
   57     This definition of "percent" differs slightly from
   58     WGL_I3D_swap_frame_usage.  In WGL_I3D_swap_frame_usage, the measurement
   59     is taken from the completion of one swap to the issuance of the next.
   60     This representation may not be as useful as measuring between
   61     completions, as a significant amount of time may pass between the
   62     issuance of a swap and the swap actually occurring.
   63 
   64     There is also a mechanism to determine whether a frame swap was
   65     missed.
   66 
   67 New Procedures and Functions
   68 
   69     int glXGetFrameUsageMESA(Display *dpy,
   70                              GLXDrawable drawable,
   71                              float *usage)
   72 
   73     int glXBeginFrameTrackingMESA(Display *dpy,
   74                                   GLXDrawable drawable)
   75 
   76     int glXEndFrameTrackingMESA(Display *dpy,
   77                                 GLXDrawable drawable)
   78 
   79     int glXQueryFrameTrackingMESA(Display *dpy,
   80                                   GLXDrawable drawable,
   81                   int64_t *swapCount,
   82                                   int64_t *missedFrames,
   83                                   float *lastMissedUsage)
   84 
   85 New Tokens
   86 
   87     None
   88 
   89 Additions to Chapter 2 of the 1.4 GL Specification (OpenGL Operation)
   90 
   91     None
   92 
   93 Additions to Chapter 3 of the 1.4 GL Specification (Rasterization)
   94 
   95     None
   96 
   97 Additions to Chapter 4 of the 1.4 GL Specification (Per-Fragment Operations
   98 and the Framebuffer)
   99 
  100     None
  101 
  102 Additions to Chapter 5 of the 1.4 GL Specification (Special Functions)
  103 
  104     None
  105 
  106 Additions to Chapter 6 of the 1.4 GL Specification (State and State Requests)
  107 
  108     None
  109 
  110 Additions to the GLX 1.3 Specification
  111 
  112     The frame usage is measured as the percentage of the swap period elapsed
  113     between two buffer-swap operations being committed.  In unextended GLX the
  114     swap period is the vertical refresh time.  If SGI_swap_control or
  115     MESA_swap_control are supported, the swap period is the vertical refresh
  116     time multiplied by the swap interval (or one if the swap interval is set
  117     to zero).
  118     
  119     If OML_sync_control is supported, the swap period is the vertical
  120     refresh time multiplied by the divisor parameter to
  121     glXSwapBuffersMscOML.  The frame usage in this case is less than 1.0 if
  122     the swap is committed before target_msc, and is greater than or equal to
  123     1.0 otherwise.  The actual usage value is based on the divisor and is
  124     never less than 0.0.
  125 
  126        int glXBeginFrameTrackingMESA(Display *dpy,
  127                                      GLXDrawable drawable,
  128                      float *usage)
  129 
  130     glXGetFrameUsageMESA returns a floating-point value in <usage>
  131     that represents the current swap usage, as defined above.
  132 
  133     Missed frame swaps can be tracked by calling the following function:
  134 
  135        int glXBeginFrameTrackingMESA(Display *dpy,
  136                                      GLXDrawable drawable)
  137 
  138     glXBeginFrameTrackingMESA resets a "missed frame" count and
  139     synchronizes with the next frame vertical sync before it returns.
  140     If a swap is missed based in the rate control specified by the
  141     <interval> set by glXSwapIntervalSGI or the default swap of once
  142     per frame, the missed frame count is incremented.
  143 
  144     The current missed frame count and total number of swaps since
  145     the last call to glXBeginFrameTrackingMESA can be obtained by
  146     calling the following function:
  147 
  148        int glXQueryFrameTrackingMESA(Display *dpy,
  149                                      GLXDrawable drawable,
  150                      int64_t *swapCount,
  151                                      int64_t *missedFrames,
  152                                      float *lastMissedUsage)
  153 
  154     The location pointed to by <swapCount> will be updated with the
  155     number of swaps that have been committed.  This value may not match the
  156     number of swaps that have been requested since swaps may be
  157     queued by the implementation.  This function can be called at any
  158     time and does not synchronize to vertical blank.
  159 
  160     The location pointed to by <missedFrames> will contain the number
  161     swaps that missed the specified frame.  The frame usage for the
  162     last missed frame is returned in the location pointed to by
  163     <lastMissedUsage>.
  164 
  165     Frame tracking is disabled by calling the function
  166 
  167        int glXEndFrameTrackingMESA(Display *dpy,
  168                                    GLXDrawable drawable)
  169 
  170     This function will not return until all swaps have occurred.  The
  171     application can call glXQueryFrameTrackingMESA for a final swap and
  172     missed frame count.
  173 
  174     If these functions are successful, zero is returned.  If the context
  175     associated with dpy and drawable is not a direct context,
  176     GLX_BAD_CONTEXT is returned.
  177 
  178 Errors
  179 
  180     If the function succeeds, zero is returned.  If the function
  181     fails, one of the following error codes is returned:
  182 
  183        GLX_BAD_CONTEXT         The current rendering context is not a direct
  184                        context.
  185 
  186 GLX Protocol
  187 
  188     None.  This extension only extends to direct rendering contexts.
  189 
  190 New State
  191 
  192     None
  193 
  194 New Implementation Dependent State
  195 
  196     None
  197 
  198 Revision History
  199 
  200     1.1,  5/1/03   Added contact information.
  201     1.0,  3/17/03  Initial version based on WGL_I3D_swap_frame_usage.