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 deterine 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 occuring. 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 commited. In unextened 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 commited 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 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 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 callling the following function: int glXQueryFrameTrackingMESA(Display *dpy, GLXDrawable drawable, int64_t *swapCount, int64_t *missedFrames, float *lastMissedUsage) The location pointed to by will be updated with the number of swaps that have been commited. 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 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 . 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 succesful, 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.