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| -rw-r--r-- | src/gallium/docs/source/context.rst | 25 |
1 files changed, 17 insertions, 8 deletions
diff --git a/src/gallium/docs/source/context.rst b/src/gallium/docs/source/context.rst index b0229c70f20..25a3245066c 100644 --- a/src/gallium/docs/source/context.rst +++ b/src/gallium/docs/source/context.rst @@ -179,16 +179,25 @@ the mode of the primitive and the vertices to be fetched, in the range between Every instance with instanceID in the range between ``start_instance`` and ``start_instance``+``instance_count``-1, inclusive, will be drawn. -All vertex indices must fall inside the range given by ``min_index`` and -``max_index``. In case non-indexed draw, ``min_index`` should be set to +If there is an index buffer bound, and ``indexed`` field is true, all vertex +indices will be looked up in the index buffer. + +In indexed draw, ``min_index`` and ``max_index`` respectively provide a lower +and upper bound of the indices contained in the index buffer inside the range +between ``start`` to ``start``+``count``-1. This allows the driver to +determine which subset of vertices will be referenced during te draw call +without having to scan the index buffer. Providing a over-estimation of the +the true bounds, for example, a ``min_index`` and ``max_index`` of 0 and +0xffffffff respectively, must give exactly the same rendering, albeit with less +performance due to unreferenced vertex buffers being unnecessarily DMA'ed or +processed. Providing a underestimation of the true bounds will result in +undefined behavior, but should not result in program or system failure. + +In case of non-indexed draw, ``min_index`` should be set to ``start`` and ``max_index`` should be set to ``start``+``count``-1. -``index_bias`` is a value added to every vertex index before fetching vertex -attributes. It does not affect ``min_index`` and ``max_index``. - -If there is an index buffer bound, and ``indexed`` field is true, all vertex -indices will be looked up in the index buffer. ``min_index``, ``max_index``, -and ``index_bias`` apply after index lookup. +``index_bias`` is a value added to every vertex index after lookup and before +fetching vertex attributes. When drawing indexed primitives, the primitive restart index can be used to draw disjoint primitive strips. For example, several separate |