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shader_recompiler: Add subpixel offset for correct rounding at ImageGather

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On AMD a subpixel offset of 1/512 of the texel size is applied to the texture coordinates at a ImageGather call to ensure the rounding at the texel centers is done the same way as in Maxwell or other Nvidia architectures.
See https://www.reedbeta.com/blog/texture-gathers-and-coordinate-precision/ for more details why this might be necessary.

This should fix shadow artifacts at object edges in Zelda: Breath of the Wild (#9957, #6956).
This commit is contained in:
Wollnashorn 2023-04-05 01:29:46 +02:00
parent bbdfe1fab1
commit 780240e697
9 changed files with 86 additions and 0 deletions
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29
src/shader_recompiler/backend/glsl/emit_glsl_image.cpp
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@ -143,6 +143,21 @@ IR::Inst* PrepareSparse(IR::Inst& inst) {
}
return sparse_inst;
}
std::string ImageGatherSubpixelOffset(const IR::TextureInstInfo& info, std::string_view texture,
std::string_view coords) {
switch (info.type) {
case TextureType::Color2D:
case TextureType::Color2DRect:
return fmt::format("{}+vec2(0.001953125)/vec2(textureSize({}, 0))", coords, texture);
case TextureType::ColorArray2D:
case TextureType::ColorCube:
return fmt::format("vec3({0}.xy+vec2(0.001953125)/vec2(textureSize({1}, 0)),{0}.z)", coords,
texture);
default:
return std::string{coords};
}
}
} // Anonymous namespace
void EmitImageSampleImplicitLod(EmitContext& ctx, IR::Inst& inst, const IR::Value& index,
@ -340,6 +355,13 @@ void EmitImageGather(EmitContext& ctx, IR::Inst& inst, const IR::Value& index,
LOG_WARNING(Shader_GLSL, "Device does not support sparse texture queries. STUBBING");
ctx.AddU1("{}=true;", *sparse_inst);
}
std::string coords_with_subpixel_offset;
if (ctx.profile.need_gather_subpixel_offset) {
// Apply a subpixel offset of 1/512 the texel size of the texture to ensure same rounding on
// AMD hardware as on Maxwell or other Nvidia architectures.
coords_with_subpixel_offset = ImageGatherSubpixelOffset(info, texture, coords);
coords = coords_with_subpixel_offset;
}
if (!sparse_inst || !supports_sparse) {
if (offset.IsEmpty()) {
ctx.Add("{}=textureGather({},{},int({}));", texel, texture, coords,
@ -387,6 +409,13 @@ void EmitImageGatherDref(EmitContext& ctx, IR::Inst& inst, const IR::Value& inde
LOG_WARNING(Shader_GLSL, "Device does not support sparse texture queries. STUBBING");
ctx.AddU1("{}=true;", *sparse_inst);
}
std::string coords_with_subpixel_offset;
if (ctx.profile.need_gather_subpixel_offset) {
// Apply a subpixel offset of 1/512 the texel size of the texture to ensure same rounding on
// AMD hardware as on Maxwell or other Nvidia architectures.
coords_with_subpixel_offset = ImageGatherSubpixelOffset(info, texture, coords);
coords = coords_with_subpixel_offset;
}
if (!sparse_inst || !supports_sparse) {
if (offset.IsEmpty()) {
ctx.Add("{}=textureGather({},{},{});", texel, texture, coords, dref);