shader type coherence

[koubaa]

Runtime layout validation. Slang provides a reflection API that reports struct layouts (size, field offsets, field types) after compilation. Goldy could query this at shader load time and compare against the Rust-side layout (derivable via std::mem::size_of, std::mem::offset_of!, etc.). A mismatch would produce a clear error at startup rather than silent corruption. This is the most practical near-term improvement.

Static reflection and compile-time checking. If Rust's type metadata (field names, types, offsets) could be compared against Slang's reflection data at compile time — perhaps via a build script that compiles the shader, extracts reflection, and asserts layout compatibility — the mismatch would become a build error. This is the ideal end state but requires tooling that doesn't exist yet.

The cross-language type coherence problem is fundamental to any multi-language GPU stack. Goldy's current approach (convention + testing) works but scales poorly as the number of shared types grows. Runtime reflection validation is the likely next step.

[koubaa]

Shader reflection for binding type strides (longer-term)

When add_compute_shader compiles a Slang shader, Slang's reflection API can report the type of each binding slot (e.g., RWStructuredBuffer<IndirectCount> at slot 1 → element size 16). Store this per-shader:

struct GoldyShader {
    pipeline: ComputePipeline,
    bindings: Vec<BindType>,
    binding_strides: Vec<Option<u32>>,  // NEW: from Slang reflection
}

Then at dispatch time, compare the shader's expected stride for each binding against the actual descriptor stride of the bound buffer. If they mismatch, it's an immediate error:

// At dispatch time in goldy_engine.rs:
if cfg!(debug_assertions) {
    for (i, expected_stride) in shader.binding_strides.iter().enumerate() {
        if let Some(expected) = expected_stride {
            if let Some(actual) = bound_buffer_stride(i) {
                assert_eq!(*expected, actual,
                    "binding {i}: shader expects stride {expected} but buffer has {actual}");
            }
        }
    }
}