Intel Skylake+ On Mesa Wires In Two More OpenGL Extensions
Written by Michael Larabel in Intel on 7 December 2016 at 06:35 AM EST. Add A Comment
Intel's Mesa driver has wired in support for two more OpenGL extensions not part of an official OpenGL specification release. These two new extensions are supported for Skylake and newer.

First, the Intel Mesa driver now supports INTEL_conservative_rasterization. The INTEL_conservative_rasterization was introduced earlier this year by Intel. "Regular rasterization includes fragments with at least one sample covered by a polygon. Conservative rasterization includes all fragments that are at least partially covered by the polygon. In some use cases, it is also important to know if a fragment is fully covered by a polygon, i.e. if all parts of the fragment are within the polygon. An application may, for example, want to process fully covered fragments different from the "edge" pixels. This extension adds an option for the fragment shader to receive this information via gl_SampleMaskIn[]. This extension affects only polygons in FILL mode and specifically does not imply any changes in processing of lines or points. Conservative rasterization automatically disables polygon antialiasing rasterization if enabled by POLYGON_SMOOTH," more details via the registry.

The other new extension is ARB_post_depth_coverage, also just for Intel Gen9 graphics and newer. This extension was ratified by Khronos in 2015 as explained via the registry, "This extension allows the fragment shader to control whether values in gl_SampleMaskIn[] reflect the coverage after application of the early depth and stencil tests."

Intel's i965 driver is the first within Mesa for supporting the INTEL_conservative_rasterization and ARB_post_depth_coverage OpenGL extensions.
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