The tessellator ignores all writes to gl_TessLevelInner and gl_TessLevelOuter by the tessellation control shader except except those done by the last TCS invocation (gl_InvocationID == patch output vertices - 1). This results in no primitives being generated unless all entries of gl_TessLevelOuter are written in that invocation (the 'initial' values seem to be 0 for gl_TessLevelOuter and 1 for gl_TessLevelInner). Additionally, barrier() does not synchronize changes to the gl_TessLevel* between TCS invocations. Neither of these problems can be reproduced with user-defined 'patch out' variables - writes by any TCS invocation are visible in the evaluation shader and barrier() makes them visible to the other TCS invocations. GPU: Radeon HD 7950 (TAHITI) Mesa: 10.7.0-devel (git-9deb614) LLVM: r243203
Created attachment 117373 [details] Tessellation test case I have attached a test case for this. It can be compiled and run using: $ sh tessellation.cpp Use the arrow keys to change which TCS invocation writes to gl_TessLevel* (or use space/enter to toggle between the first and the last). It should display a yellow grid no matter what TCS invocation is selected but instead displays a green grid for invocation 3 and nothing for all other invocations.
I can confirm that the patch "radeonsi: before storing tess levels, load them from LDS instead of temporary" on the mailing list fixes the issue.
Fixed by 60159bcfc66a067b50da06f5cabfa20d72e89. Closing.
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