The Nouveau indirect drawing work developed by Christoph Bumiller and reviewed by Ilia Mirkin was committed on Tuesday night. The work specifically allows GL_ARB_draw_indirect support to be enabled from the OpenGL 4.0 specification and GL_ARB_multi_draw_indirect from the OpenGL 4.3 specification. Up to now, the Intel classic Mesa DRI driver was the only other Mesa/Gallium3D driver supporting these indirect extensions -- the Radeon driver doesn't yet support these GL4 extensions.
GL_ARB_draw_indirect - "This extension provides a mechanism for supplying the arguments to a DrawArraysInstanced or DrawElementsInstancedBaseVertex from buffer object memory. This is not particularly useful for applications where the CPU knows the values of the arguments beforehand, but is helpful when the values will be generated on the GPU through any mechanism that can write to a buffer object including image stores, atomic counters, or compute interop. This allows the GPU to consume these arguments without a round-trip to the CPU or the expensive synchronization that would involve. This is similar to the DrawTransformFeedbackEXT command from EXT_transform_feedback2, but offers much more flexibility in both generating the arguments and in the type of Draws that can be accomplished."
GL_ARB_multi_draw_indirect - "The ARB_draw_indirect extension (included in OpenGL 4.0) introduced mechanisms whereby the parameters for a draw function may be provided in a structure contained in a buffer object rather than as parameters to the drawing procedure. This is known as an indirect draw and is exposed as two new functions, glDrawArraysIndirect and glDrawElementsIndirect. Each of these functions generates a single batch of primitives."
Adding the indirect drawing support amounted to just over 200 lines of new code in the NVC0 Nouveau Gallium3D driver and this work will be found in the upcoming Mesa 10.3 release.