Ian's buffer swap extensions
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Brian Paul
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1a8d64e6e9
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09b00c5ded
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Name
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MESA_swap_control
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Name Strings
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GLX_MESA_swap_control
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Contact
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Ian Romanick, IBM (idr 'at' us.ibm.com)
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Status
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Deployed in DRI drivers post-XFree86 4.3.
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Version
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Date: 3/17/2003 Revision: 1.0
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Number
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???
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Dependencies
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None
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Based on GLX_SGI_swap_control version 1.9 and WGL_EXT_swap_control
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version 1.5.
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Overview
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This extension allows an application to specify a minimum periodicity
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of color buffer swaps, measured in video frame periods.
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New Procedures and Functions
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int glXSwapIntervalMESA(int interval)
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int glXGetSwapIntervalMESA(void)
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New Tokens
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None
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Additions to Chapter 2 of the 1.4 GL Specification (OpenGL Operation)
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None
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Additions to Chapter 3 of the 1.4 GL Specification (Rasterization)
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None
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Additions to Chapter 4 of the 1.4 GL Specification (Per-Fragment Operations
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and the Framebuffer)
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None
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Additions to Chapter 5 of the 1.4 GL Specification (Special Functions)
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None
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Additions to Chapter 6 of the 1.4 GL Specification (State and State Requests)
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None
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Additions to the GLX 1.3 Specification
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[Add the following to Section 3.3.10 of the GLX Specification (Double
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Buffering)]
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glXSwapIntervalMESA specifies the minimum number of video frame periods
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per buffer swap. (e.g. a value of two means that the color buffers
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will be swapped at most every other video frame.) A return value
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of zero indicates success; otherwise an error occurred. The interval
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takes effect when glXSwapBuffers is first called subsequent to the
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glXSwapIntervalMESA call.
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A video frame period is the time required by the monitor to display a
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full frame of video data. In the case of an interlaced monitor,
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this is typically the time required to display both the even and odd
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fields of a frame of video data.
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If <interval> is set to a value of 0, buffer swaps are not synchron-
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ized to a video frame. The <interval> value is silently clamped to
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the maximum implementation-dependent value supported before being
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stored.
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The swap interval is not part of the render context state. It cannot
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be pushed or popped. The current swap interval for the window
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associated with the current context can be obtained by calling
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glXGetSwapIntervalMESA. The default swap interval is 1.
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On XFree86, setting the environment variable LIBGL_NO_VSYNC sets the
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swap interval to 0.
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Errors
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glXSwapIntervalMESA returns GLX_BAD_VALUE if parameter <interval> is
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less than zero.
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glXSwapIntervalMESA returns GLX_BAD_CONTEXT if there is no current
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GLXContext.
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GLX Protocol
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None. This extension only extends to direct rendering contexts.
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New State
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Get Value Get Command Type Initial Value
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--------- ----------- ---- -------------
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[swap interval] GetSwapInterval Z+ 1
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New Implementation Dependent State
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None
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@ -0,0 +1,196 @@
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Name
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MESA_swap_frame_usage
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Name Strings
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GLX_MESA_swap_frame_usage
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Contact
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Ian Romanick, IBM (idr 'at' us.ibm.com)
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Status
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Deployed in DRI drivers post-XFree86 4.3.
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Version
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Date: 3/17/2003 Revision: 1.0
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Number
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???
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Dependencies
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GLX_SGI_swap_control affects the definition of this extension.
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GLX_MESA_swap_control affects the definition of this extension.
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GLX_OML_sync_control affects the definition of this extension.
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Based on WGL_I3D_swap_frame_usage version 1.3.
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Overview
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This extension allows an application to deterine what portion of the
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swap period has elapsed since the last swap operation completed. The
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"usage" value is a floating point value on the range [0,max] which is
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calculated as follows:
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td
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percent = ----
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tf
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where td is the time measured from the last completed buffer swap (or
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call to enable the statistic) to when the next buffer swap completes, tf
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is the entire time for a frame which may be multiple screen refreshes
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depending on the swap interval as set by the GLX_SGI_swap_control or
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GLX_OML_sync_control extensions.
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The value, percent, indicates the amount of time spent between the
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completion of the two swaps. If the value is in the range [0,1], the
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buffer swap occurred within the time period required to maintain a
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constant frame rate. If the value is in the range (1,max], a constant
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frame rate was not achieved. The value indicates the number of frames
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required to draw.
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This definition of "percent" differs slightly from
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WGL_I3D_swap_frame_usage. In WGL_I3D_swap_frame_usage, the measurement
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is taken from the completion of one swap to the issuance of the next.
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This representation may not be as useful as measuring between
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completions, as a significant amount of time may pass between the
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issuance of a swap and the swap actually occuring.
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There is also a mechanism to determine whether a frame swap was
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missed.
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New Procedures and Functions
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int glXGetFrameUsageMESA(Display *dpy,
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GLXDrawable drawable,
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float *usage)
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int glXBeginFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable)
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int glXEndFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable)
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int glXQueryFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable,
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int64_t *swapCount,
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int64_t *missedFrames,
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float *lastMissedUsage)
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New Tokens
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None
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Additions to Chapter 2 of the 1.4 GL Specification (OpenGL Operation)
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None
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Additions to Chapter 3 of the 1.4 GL Specification (Rasterization)
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None
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Additions to Chapter 4 of the 1.4 GL Specification (Per-Fragment Operations
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and the Framebuffer)
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None
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Additions to Chapter 5 of the 1.4 GL Specification (Special Functions)
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None
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Additions to Chapter 6 of the 1.4 GL Specification (State and State Requests)
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None
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Additions to the GLX 1.3 Specification
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The frame usage is measured as the percentage of the swap period elapsed
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between two buffer-swap operations being commited. In unextened GLX the
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swap period is the vertical refresh time. If SGI_swap_control or
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MESA_swap_control are supported, the swap period is the vertical refresh
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time multiplied by the swap interval (or one if the swap interval is set
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to zero).
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If OML_sync_control is supported, the swap period is the vertical
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refresh time multiplied by the divisor parameter to
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glXSwapBuffersMscOML. The frame usage in this case is less than 1.0 if
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the swap is commited before target_msc, and is greater than or equal to
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1.0 otherwise. The actual usage value is based on the divisor and is
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never less than 0.0.
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int glXBeginFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable,
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float *usage)
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glXGetFrameUsageMESA returns a floating-point value in <usage>
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that represents the current swap usage, as defined above.
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Missed frame swaps can be tracked by calling the following function:
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int glXBeginFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable)
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glXBeginFrameTrackingMESA resets a "missed frame" count and
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synchronizes with the next frame vertical sync before it returns.
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If a swap is missed based in the rate control specified by the
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<interval> set by glXSwapIntervalSGI or the default swap of once
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per frame, the missed frame count is incremented.
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The current missed frame count and total number of swaps since
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the last call to glXBeginFrameTrackingMESA can be obtained by
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callling the following function:
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int glXQueryFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable,
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int64_t *swapCount,
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int64_t *missedFrames,
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float *lastMissedUsage)
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The location pointed to by <swapCount> will be updated with the
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number of swaps that have been commited. This value may not match the
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number of swaps that have been requested since swaps may be
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queued by the implementation. This function can be called at any
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time and does not synchronize to vertical blank.
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The location pointed to by <missedFrames> will contain the number
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swaps that missed the specified frame. The frame usage for the
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last missed frame is returned in the location pointed to by
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<lastMissedUsage>.
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Frame tracking is disabled by calling the function
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int glXEndFrameTrackingMESA(Display *dpy,
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GLXDrawable drawable)
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This function will not return until all swaps have occurred. The
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application can call glXQueryFrameTrackingMESA for a final swap and
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missed frame count.
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If these functions are succesful, zero is returned. If the context
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associated with dpy and drawable is not a direct context,
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GLX_BAD_CONTEXT is returned.
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Errors
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If the function succeeds, zero is returned. If the function
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fails, one of the following error codes is returned:
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GLX_BAD_CONTEXT The current rendering context is not a direct
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context.
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GLX Protocol
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None. This extension only extends to direct rendering contexts.
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New State
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None
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New Implementation Dependent State
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None
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