RadeonSI Gets OpenGL 4.5 Derivative Control Support

Written by Michael Larabel in Radeon on 25 July 2015 at 09:26 PM EDT. 35 Comments
The latest OpenGL 4+ activity in Mesa this week is a Saturday commit landing another OpenGL 4.5 extension for AMD's RadeonSI Gallium3D driver for GCN graphics processors.

Dave Airlie of Red Hat implemented support for the ARB_derivative_control extension on RadeonSI. ARB_derivative_control is needed by OpenGL 4.5 and described by OpenGL.org as "provides control over the spacial granularity at which the underlying implementation computes derivatives. For example, for the coarse-granularity derivative, a single x derivative could be computed for each 2x2 group of pixels, using that same derivative value for all 4 pixels. For the fine-granularity derivative, two derivatives could be computed for each 2x2 group of pixels; one for the top row and one for the bottom row. Implementations vary somewhat on how this is done."

The Intel i965 DRI, Nouveau NV50 / NVC0, and Radeon R600 drivers had already supported this extension. This is just another step towards OpenGL 4.5 albeit there's still many other larger work items on OpenGL 4.3/4.4/4.5 before that latest Khronos specification will be supported. At least Mesa is still getting in shape for hopefully reaching OpenGL 4.2 compliance prior to its next release in September.
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