| Bug ID | 91461 |
|---|---|
| Summary | gl_TessLevel* writes have no effect for all but the last TCS invocation |
| Product | Mesa |
| Version | git |
| Hardware | Other |
| OS | All |
| Status | NEW |
| Severity | normal |
| Priority | medium |
| Component | Drivers/Gallium/radeonsi |
| Assignee | dri-devel@lists.freedesktop.org |
| Reporter | daniel@constexpr.org |
| QA Contact | dri-devel@lists.freedesktop.org |
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.
| What | Removed | Added |
|---|---|---|
| Status | NEW | RESOLVED |
| Resolution | --- | FIXED |
Fixed by 60159bcfc66a067b50da06f5cabfa20d72e89. Closing.