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| -rw-r--r-- | src/gallium/docs/source/context.rst | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/src/gallium/docs/source/context.rst b/src/gallium/docs/source/context.rst index d394f5b4f1..b7b625d25e 100644 --- a/src/gallium/docs/source/context.rst +++ b/src/gallium/docs/source/context.rst @@ -149,6 +149,42 @@ Queries can be created with ``create_query`` and deleted with use ``end_query`` to stop the query. Finally, ``get_query_result`` is used to retrieve the results. +A common type of query is the occlusion query which counts the number of +fragments/pixels which are written to the framebuffer (and not culled by +Z/stencil/alpha testing or shader KILL instructions). + + +Conditional Rendering +^^^^^^^^^^^^^^^^^^^^^ + +A drawing command can be skipped depending on the outcome of a query +(typically an occlusion query). The ``render_condition`` function specifies +the query which should be checked prior to rendering anything. + +If ``render_condition`` is called with ``query`` = NULL, conditional +rendering is disabled and drawing takes place normally. + +If ``render_condition`` is called with a non-null ``query`` subsequent +drawing commands will be predicated on the outcome of the query. If +the query result is zero subsequent drawing commands will be skipped. + +If ``mode`` is PIPE_RENDER_COND_WAIT the driver will wait for the +query to complete before deciding whether to render. + +If ``mode`` is PIPE_RENDER_COND_NO_WAIT and the query has not yet +completed, the drawing command will be executed normally. If the query +has completed, drawing will be predicated on the outcome of the query. + +If ``mode`` is PIPE_RENDER_COND_BY_REGION_WAIT or +PIPE_RENDER_COND_BY_REGION_NO_WAIT rendering will be predicated as above +for the non-REGION modes but in the case that an occulusion query returns +a non-zero result, regions which were occluded may be ommitted by subsequent +drawing commands. This can result in better performance with some GPUs. +Normally, if the occlusion query returned a non-zero result subsequent +drawing happens normally so fragments may be generated, shaded and +processed even where they're known to be obscured. + + Flushing ^^^^^^^^ |