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'''OpenGL extension APPLE.fence |
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This module customises the behaviour of the |
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OpenGL.raw.GL.APPLE.fence to provide a more |
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Python-friendly API |
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Overview (from the spec) |
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This extension is provided a finer granularity of synchronizing GL command |
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completion than offered by standard OpenGL, which currently offers only two |
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mechanisms for synchronization: Flush and Finish. Since Flush merely assures |
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the user that the commands complete in a finite (though undetermined) amount |
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of time, it is, thus, of only modest utility. Finish, on the other hand, |
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stalls CPU execution until all pending GL commands have completed forcing |
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completely synchronous operation, which most often not the desired result. |
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This extension offers a middle ground - the ability to "finish" a subset of |
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the command stream, and the ability to determine whether a given command has |
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completed or not. |
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This extension introduces the concept of a "fence" to the OpenGL command |
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stream with SetFenceAPPLE. Once the fence is inserted into the command |
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stream, it can be tested for its completion with TestFenceAPPLE. Moreover, |
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the application may also request a partial Finish up to a particular "fence" |
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using the FinishFenceAPPLE command -- that is, all commands prior to the |
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fence will be forced to complete until control is returned to the calling |
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process. These new mechanisms allow for synchronization between the host |
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CPU and the GPU, which may be accessing the same resources (typically |
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memory). |
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Fences are created and deleted, as are other objects in OpenGL, specifically |
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with GenFencesAPPLE and DeleteFencesAPPLE. The former returns a list of |
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unused fence names and the later deletes the provided list of fence names. |
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In addition to being able to test or finish a fence this extension allows |
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testing for other types of completion, including texture objects, vertex |
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array objects, and draw pixels. This allows the client to use |
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TestObjectAPPLE or FinishObjectAPPLE with FENCE_APPLE, TEXTURE, |
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VERTEX_ARRAY, or DRAW_PIXELS_APPLE with the same type of results as |
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TestFenceAPPLE and FinishFenceAPPLE. Specifically, using the FENCE_APPLE |
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type is equivalent to calling TestFenceAPPLE or FinishFenceAPPLE with the |
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particular fence name. Using TEXTURE as the object type tests or waits for |
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completion of a specific texture, meaning when there are no pending |
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rendering commands which use that texture object. Using the VERTEX_ARRAY |
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type will test or wait for drawing commands using that particular vertex |
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array object name. Finally, DRAW_PIXELS_APPLE will wait or test for |
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completion of all pending DrawPixels commands. These tests and finishes |
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operate with the same limitations and results as test and finish fence. |
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One use of this extension is in conjunction with APPLE_vertex_array_range to |
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determine when graphics hardware has completed accessing vertex data from a |
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vertex array range. Once a fence has been tested TRUE or finished, all |
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vertex indices issued before the fence must have completed being accessed. |
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This ensures that the vertex data memory corresponding to the issued vertex |
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indices can be safely modified (assuming no other outstanding vertex indices |
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are issued subsequent to the fence). |
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The official definition of this extension is available here: |
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http://www.opengl.org/registry/specs/APPLE/fence.txt |
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''' |
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from OpenGL import platform, constant, arrays |
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from OpenGL import extensions, wrapper |
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import ctypes |
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from OpenGL.raw.GL import _types, _glgets |
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from OpenGL.raw.GL.APPLE.fence import * |
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from OpenGL.raw.GL.APPLE.fence import _EXTENSION_NAME |
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def glInitFenceAPPLE(): |
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'''Return boolean indicating whether this extension is available''' |
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from OpenGL import extensions |
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return extensions.hasGLExtension( _EXTENSION_NAME ) |
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glGenFencesAPPLE=wrapper.wrapper(glGenFencesAPPLE).setOutput( |
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'fences',size=lambda x:(x,),pnameArg='n',orPassIn=True |
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) |
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glDeleteFencesAPPLE=wrapper.wrapper(glDeleteFencesAPPLE).setInputArraySize( |
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'fences', None |
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) |
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