michal wrote on 2010-01-12 19:02:
Keith,
I would like to merge this branch to master soon.
It adds new entrypoints to pipe_context -- draw_arrays_instanced() and
draw_elements_instanced(). A new system value is introduced to TGSI that
allows vertex shaders to access current instance ID.
The new entrypoints are implemented in draw module, and softpipe driver
has been properly adjusted for that.
There is no capability bit defined for that -- I wasn't sure whether we
still want to go this route.
Please review, thanks.
Attached a patch that adds documentation for drawing commands, done
against master branch since instanced-arrays branch doesn't have the
gallium docs tree yet.
Thanks.
diff --git a/src/gallium/docs/source/context.rst
b/src/gallium/docs/source/context.rst
index 21f5f91..9686537 100644
--- a/src/gallium/docs/source/context.rst
+++ b/src/gallium/docs/source/context.rst
@@ -72,12 +72,64 @@ 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 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 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 value of ``instanceID`` can be read in a vertex shader through a system
+value register declared with INSTANCEID semantic name.
+
Queries
^^^^^^^
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