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[Fix] (Program): read an API colour index of zero as no override, matching the IO resolver and ProgramInterface

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swung0x48
2026-08-27 10:52:00 -04:00
parent b6d6316333
commit 3c70b4fc0f
2 changed files with 86 additions and 5 deletions
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MobileGL/MG_State/GLState/ProgramState/ProgramLinkTask.cpp
+35 -5
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@@ -1875,15 +1875,45 @@ namespace MobileGL::MG_State::GLState {
const Int location = explicitLocation != in.explicitFragDataLocation.end()
? static_cast<Int>(explicitLocation->second)
: static_cast<Int>(output.layoutLocation());
// glBindFragDataLocationIndexed wins over the shader's own qualifier, the same
// precedence the location above follows and the same one ProgramInterface applies.
// The colour INDEX, under the one precedence rule the whole codebase uses: a NON-ZERO
// glBindFragDataLocationIndexed index wins, and a zero (or absent) one falls back to
// the shader's own layout(index = N).
//
// Zero has to mean "no override" rather than "index 0", because glBindFragDataLocation
// IS glBindFragDataLocationIndexed with index 0 (GL_Program.cpp) and writes a real 0
// into this map. Reading that 0 as an override made a blanket
// `glBindFragDataLocation(prog, 0, "b")` over a shader that declares
// `layout(location = 0, index = 1) out vec4 b;` collapse b onto slot (0,0) next to the
// index-0 output and fail the link as an alias - while the IO resolver had left b's
// qualifier at 1, the SPIR-V still carried Index 1, and glGetProgramResourceLocationIndex
// still answered 1. Validation was rejecting a program the backend had already emitted
// correctly, which is the one case where this branch can change the answer at all: this
// runs AFTER ShaderCompiler::LinkProgram/mapIO, so for every other shape the qualifier
// already carries the resolver's verdict.
//
// The two other consumers spell the same rule: TMglGlslIoResolver only writes the API
// index into the qualifier when it is non-zero, and ProgramInterface falls back to
// type.layoutIndex when GetFragmentDataIndex answers 0. All three now agree.
//
// Against the spec (GL 4.6 core 15.2.3): where a fragment output's index is given by a
// shader layout qualifier, that value is used and anything bound through
// BindFragDataLocation(Indexed) is IGNORED - the same precedence layout(location) has
// over glBindAttribLocation. That is stricter than "non-zero API wins", and the two
// differ in exactly one shape: an explicit `index = 0` in the shader against an API
// index of 1, where the spec keeps 0 and this codebase takes 1. That divergence lives
// in the resolver (it decides what is emitted); it is pre-existing, out of scope here,
// and deliberately not re-litigated in a third place - matching the resolver is what
// keeps validation checking what was actually built.
Int colorIndex = 0;
if (const auto explicitIndex = in.explicitFragDataIndex.find(outputName);
explicitIndex != in.explicitFragDataIndex.end()) {
colorIndex = static_cast<Int>(explicitIndex->second);
} else if (const glslang::TType* outputType = output.getType();
outputType != nullptr && outputType->getQualifier().hasIndex()) {
colorIndex = static_cast<Int>(outputType->getQualifier().layoutIndex);
}
if (colorIndex == 0) {
if (const glslang::TType* outputType = output.getType();
outputType != nullptr && outputType->getQualifier().hasIndex()) {
colorIndex = static_cast<Int>(outputType->getQualifier().layoutIndex);
}
}
const Int span = std::max<Int>(output.size, 1);