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gallium: Document drawing commands.

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Michal Krol 2010-01-14 18:55:52 +01:00
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59
src/gallium/docs/source/context.rst
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@ -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
^^^^^^^