Cg" discussion
NVIDIA wanted to discuss their goals with Cg (although they are not offering Cg to the ARB)
Principal goals are to enable apps to use all the features of NVIDIA hardware, do rapid prototyping, and make efficient use of the underlying architecture. "Profiles" allow compiler to control what it accepts as valid programs.
Goal is that there not need to be multiple, very similar shading languages for different underlying APIs and platforms. Thus Cg is syntactially and semantically compatible with HLSL in DX9; may not be true forever, but it is today. This is a constraint on evolving the language, had to get feedback from developers and work with Microsoft.
Bimal asked about NVIDIA's interest in incorporating a high-level language directly into OpenGL, ala 3Dlabs' design. Nick says what's important is solving developers' problems, and they want a single shading language. If the market wants an integrated language, NVIDIA will support that too - but they don't think that's what developers want, and they're less excited about it. What's critical to making Cg work is having the right low-level interfaces to the underlying API, and that's where they want to concentrate their efforts.
Discussion followed on the relative effort the ARB should put into low and high level language working groups. ARB_vertex_program now represents nearly 2 year old technology; low level interfaces need to look at branching, looping, etc. constructs.
Cg backend receives a partially optimized DAG representation of the shader. Must figure out how to map onto what the backend supports.
Compatibility with DX is very important, but they're willing to weigh advantages of changes vs. cost. Cg and the proposed "OpenGL 2.0" language are similar but not identical; both look like C, and both target multiple underlying execution units. Interfaces, communication between nodes, and accessing state across nodes are different. It's very late, but not too late to contemplate merging the two languages.
