This patch series fixes bugs in the i965 w.r.t. several uses of gl_VertexID. OpenGL (desktop and ES) have the following expectations of gl_VertexID:
1. When used with BaseVertex drawing commands, gl_VertexID will include the value of basevertex. This differens from "the other API," but the change in OpenGL was based on feedback from application developers. This only affects OpenGL 3.2+. 2. When used with DrawArrays drawing commands, gl_VertexID will count from the 'start' value instead of zero. This affects OpenGL 3.0+ and OpenGL ES 3.0+. The i965 driver botched both of these for slightly different reasons. For #1, our hardware was designed with the "other API's" semantic in mind, so gl_VertexID doesn't include the basevertex value. For #2, we implement DrawArrays with a non-zero start index by reprogramming the array base offset. As a result, gl_VertexID always counts from zero. I suspect other hardware may suffer from one or both of these issues. I have sent tests to the piglit list to reproduce them. To fix both of these issues, the shader needs to know the basevertex value. A later GL extension, GL_ARB_shader_draw_parameters, adds gl_BaseVertex and gl_BaseInstance as built-in variables. I believe some hardware implements these as system values much like gl_VertexID. I started this series with the assumption that we could have a SYSTEM_VALUE_BASE_VERTEX that might come from a uniform. In the end, I couldn't make that work. I left patch 7 in the series, but we may want to remove it. I added a STATE_BASE_VERTEX uniform instead. There is now a lowering pass that converts gl_VertexID to gl_VertexIDMESA + gl_BaseVertex (backed by a uniform). Some of these names should probably be changed. I have also contemplated adding an extension that exposes the other semantic for gl_VertexID for applications that actually want that. This is primarily things that are porting content (or "bridging" content) from the other API. That, however, can happen later. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
