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132 строки
4.5 KiB
Plaintext
132 строки
4.5 KiB
Plaintext
Name
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CHROMIUM_get_sync_values
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Name Strings
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EGL_CHROMIUM_get_sync_values
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Contact
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Stéphane Marchesin, Google (marcheu 'at' google.com)
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Status
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Draft.
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Version
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Last Modified Date: N/A Revision: 1.0
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Based on GLX_OML_sync_control Revision 6.0
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Number
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???
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Dependencies
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The extension is written against the EGL 1.2 Specification, although it
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should work on other versions of these specifications. This extension
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also requires an operating system which supports CLOCK_MONOTONIC.
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Overview
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This extension provides counters which let applications know about the
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timing of the last vertical retrace. By looking at the system clock, as
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well as the refresh rate of the monitor, this should enable applications
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to predict the position of future retraces so as to schedule an optimal
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workload.
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This extension incorporates the use of three counters that provide
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the necessary synchronization. The Unadjusted System Time (or UST)
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is the 64-bit CLOCK_MONOTONIC clock; in particular this lets the
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application schedule future vertical retraces by querying this clock.
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The graphics Media Stream Counter (or graphics MSC) is a counter
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that is unique to the graphics subsystem and increments for each
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vertical retrace that occurs. The Swap Buffer Counter (SBC) is an
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attribute of an EGLSurface and is incremented each time a swap
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buffer action is performed on the associated surface.
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The use of these three counters allows the application to
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synchronize graphics rendering to vertical retraces and/or swap
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buffer actions. For example, by querying the synchronization values for
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a given surface, the application can accurately predict the timing for
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the next vertical retraces and schedule rendering accordingly.
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Issues
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None.
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IP Status
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No known issues.
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New Procedures and Functions
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Bool eglGetSyncValuesCHROMIUM(EGLDisplay dpy,
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EGLSurface surface,
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int64_t* ust,
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int64_t* msc,
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int64_t* sbc)
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New Tokens
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None
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Additions to the EGL 1.3 Specification
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eglGetSyncValuesCHROMIUM returns the current UST/MSC/SBC triple. A UST
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timestamp is obtained each time the graphics MSC is incremented.
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If this value does not reflect the value of the UST at the time the
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first scan line of the display begins passing through the video
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output port, it will be adjusted by the graphics driver to do so
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prior to being returned by any of the functions defined by this
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extension.
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This UST timestamp, together with the current graphics MSC and the
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current SBC, comprise the current UST/MSC/SBC triple. The UST,
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graphics MSC, and SBC values are not part of the render context
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state. These values cannot be pushed or popped. The graphics MSC
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value is initialized to 0 when the graphics device is initialized.
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The SBC is per-surface state and is initialized to 0 when the
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EGLSurface data structure is initialized.
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The SBC value is incremented by the graphics driver at the completion
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of each buffer swap (e.g., the pixel copy has been completed or the
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hardware register that swaps memory banks has been written). For pixel
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formats that do not contain a back buffer, the SBC will always be
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returned as 0.
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The graphics MSC value is incremented once for each screen refresh.
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For a non-interlaced display, this means that the graphics MSC value
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is incremented for each frame. For an interlaced display, it means
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that it will be incremented for each field. For a multi-monitor
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system, the monitor used to determine MSC is the one where the surface
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is located. If the surface spans multiple monitors, the monitor used
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to determine MSC is the one with the biggest coverage in pixels.
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The function eglGetSyncValuesCHROMIUM will return TRUE if the function
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completed successfully, FALSE otherwise.
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Each time eglSwapBuffer succeeds, the SBC will be increased within a
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finite time period.
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Errors
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eglGetSyncValuesCHROMIUM will return FALSE if there is no current
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EGLContext.
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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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[UST] eglGetSyncValuesCHROMIUM Z unspecified
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[MSC] eglGetSyncValuesCHROMIUM Z 0
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[SBC] eglGetSyncValuesCHROMIUM Z 0
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New Implementation Dependent State
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None
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