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gallium/docs: Improve min_index/max_index description.

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José Fonseca 2011-04-16 10:18:20 +01:00
parent 4ee40c37a0
commit bb78f6ad78
1 changed files with 17 additions and 8 deletions
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25
src/gallium/docs/source/context.rst
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@ -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