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Diffstat (limited to 'src/gallium/docs')
| -rw-r--r-- | src/gallium/docs/source/context.rst | 59 |
1 files changed, 57 insertions, 2 deletions
diff --git a/src/gallium/docs/source/context.rst b/src/gallium/docs/source/context.rst index 21f5f9111a..3183954638 100644 --- a/src/gallium/docs/source/context.rst +++ b/src/gallium/docs/source/context.rst @@ -72,12 +72,67 @@ stencil-only clears of packed depth-stencil buffers. Drawing ^^^^^^^ -``draw_arrays`` +``draw_arrays`` draws a specified primitive. -``draw_elements`` +This command is equivalent to calling ``draw_arrays_instanced`` +with ``startInstance`` set to 0 and ``instanceCount`` set to 1. + +``draw_elements`` draws a specified primitive using an optional +index buffer. + +This command is equivalent to calling ``draw_elements_instanced`` +with ``startInstance`` set to 0 and ``instanceCount`` set to 1. ``draw_range_elements`` +XXX: this is (probably) a temporary entrypoint, as the range +information should be available from the vertex_buffer state. +Using this to quickly evaluate a specialized path in the draw +module. + +``draw_arrays_instanced`` draws multiple instances of the same primitive. + +This command is equivalent to calling ``draw_elements_instanced`` +with ``indexBuffer`` set to NULL and ``indexSize`` set to 0. + +``draw_elements_instanced`` draws multiple instances of the same primitive +using an optional index buffer. + +For instanceID in the range between ``startInstance`` +and ``startInstance``+``instanceCount``-1, inclusive, draw a primitive +specified by ``mode`` and sequential numbers in the range between ``start`` +and ``start``+``count``-1, inclusive. + +If ``indexBuffer`` is not NULL, it specifies an index buffer with index +byte size of ``indexSize``. The sequential numbers are used to lookup +the index buffer and the resulting indices in turn are used to fetch +vertex attributes. + +If ``indexBuffer`` is NULL, the sequential numbers are used directly +as indices to fetch vertex attributes. + +If a given vertex element has ``instance_divisor`` set to 0, it is said +it contains per-vertex data and effective vertex attribute address needs +to be recalculated for every index. + + attribAddr = ``stride`` * index + ``src_offset`` + +If a given vertex element has ``instance_divisor`` set to non-zero, +it is said it contains per-instance data and effective vertex attribute +address needs to recalculated for every ``instance_divisor``-th instance. + + attribAddr = ``stride`` * instanceID / ``instance_divisor`` + ``src_offset`` + +In the above formulas, ``src_offset`` is taken from the given vertex element +and ``stride`` is taken from a vertex buffer associated with the given +vertex element. + +The calculated attribAddr is used as an offset into the vertex buffer to +fetch the attribute data. + +The value of ``instanceID`` can be read in a vertex shader through a system +value register declared with INSTANCEID semantic name. + Queries ^^^^^^^ |