Programmable shaders, GLSL subset and CSIR¶

Fixed and programmable pipelines¶

A fixed-function renderer exposes predefined lighting/transform operations. A programmable pipeline lets applications provide programs for stages such as vertex and fragment processing.

ChrisOS implements a defined GLSL subset rather than claiming full desktop GLSL compatibility.

Frontend¶

The shader compiler has lexer, recursive-descent parser, AST and semantic analysis. This mirrors the general compiler pipeline but targets shader-specific types, stage interfaces, builtins and execution constraints.

Errors include source location, which is necessary for usable shader tooling.

CSIR¶

Chris Shader IR is a typed representation independent of the final VirGL/TGSI transport.

GLSL subset
  ↓
AST / semantic analysis
  ↓
CSIR
  ├── TGSI emitter → VirGL
  └── interpreter → software backend

Backend independence is the key property: language semantics should not be hard-coded as strings inside one graphics driver.

Types and interfaces¶

Shader programs need stage inputs/outputs, uniforms, samplers and temporary values. Link-time matching verifies that fragment inputs correspond to compatible vertex outputs.

Matrices use GLSL column-major semantics in the shader system. CPU-side matrix representations must be converted consistently.

Control flow constraints¶

A small shader compiler can deliberately restrict dynamic complexity. Current documentation records bounded compile-time unrolling for certain for loops and inlining rules for user functions. Unsupported constructs should fail explicitly rather than silently generate wrong shaders.

TGSI backend¶

VirGL in the current project consumes TGSI text generated from verified CSIR. TGSI is transport/backend representation, not the public shader API exposed to ChrisC.

This separation prevents applications from depending directly on virglrenderer-specific details.

Software backend¶

sh_exec.c interprets the same CSIR. The small software triangle path can exercise vertex/fragment programs with perspective-correct varyings.

Cross-backend tests are valuable because both backends consume the same IR. Differences reveal either backend bugs or underspecified semantics.

ChrisC API¶

The language-facing functions create/drop shaders and programs, attach/link, query diagnostics and set uniforms/samplers. Handles belong to the owning language slot and are destroyed on slot teardown.

Resource ownership is therefore integrated with shader API design.

Mine Chris boundary¶

The world shader pair is compiled and used by a VirGL proof draw, but the Mine Chris voxel renderer still follows the software scene path at the documented revision. Shader readiness and game migration are separate milestones.