1 files changed, 30 insertions, 0 deletions
diff --git a/src/shader_recompiler/backend/spirv/emit_spirv_image.cpp b/src/shader_recompiler/backend/spirv/emit_spirv_image.cpp
index 02073c420..7d901c04b 100644
--- a/src/shader_recompiler/backend/spirv/emit_spirv_image.cpp
+++ b/src/shader_recompiler/backend/spirv/emit_spirv_image.cpp
@@ -261,6 +261,30 @@ Id BitTest(EmitContext& ctx, Id mask, Id bit) {
     const Id bit_value{ctx.OpBitwiseAnd(ctx.U32[1], shifted, ctx.Const(1u))};
     return ctx.OpINotEqual(ctx.U1, bit_value, ctx.u32_zero_value);
 }
+
+Id ImageGatherSubpixelOffset(EmitContext& ctx, const IR::TextureInstInfo& info, Id texture,
+                             Id coords) {
+    // 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.
+    const auto calculate_coords{[&](size_t dim) {
+        const Id nudge{ctx.Const(0x1p-9f)};
+        const Id image_size{ctx.OpImageQuerySizeLod(ctx.U32[dim], texture, ctx.u32_zero_value)};
+        Id offset{dim == 2 ? ctx.ConstantComposite(ctx.F32[dim], nudge, nudge)
+                           : ctx.ConstantComposite(ctx.F32[dim], nudge, nudge, ctx.f32_zero_value)};
+        offset = ctx.OpFDiv(ctx.F32[dim], offset, ctx.OpConvertUToF(ctx.F32[dim], image_size));
+        return ctx.OpFAdd(ctx.F32[dim], coords, offset);
+    }};
+    switch (info.type) {
+    case TextureType::Color2D:
+    case TextureType::Color2DRect:
+        return calculate_coords(2);
+    case TextureType::ColorArray2D:
+    case TextureType::ColorCube:
+        return calculate_coords(3);
+    default:
+        return coords;
+    }
+}
 } // Anonymous namespace
 
 Id EmitBindlessImageSampleImplicitLod(EmitContext&) {
@@ -423,6 +447,9 @@ Id EmitImageGather(EmitContext& ctx, IR::Inst* inst, const IR::Value& index, Id
                    const IR::Value& offset, const IR::Value& offset2) {
     const auto info{inst->Flags<IR::TextureInstInfo>()};
     const ImageOperands operands(ctx, offset, offset2);
+    if (ctx.profile.need_gather_subpixel_offset) {
+        coords = ImageGatherSubpixelOffset(ctx, info, TextureImage(ctx, info, index), coords);
+    }
     return Emit(&EmitContext::OpImageSparseGather, &EmitContext::OpImageGather, ctx, inst,
                 ctx.F32[4], Texture(ctx, info, index), coords, ctx.Const(info.gather_component),
                 operands.MaskOptional(), operands.Span());
@@ -432,6 +459,9 @@ Id EmitImageGatherDref(EmitContext& ctx, IR::Inst* inst, const IR::Value& index,
                        const IR::Value& offset, const IR::Value& offset2, Id dref) {
     const auto info{inst->Flags<IR::TextureInstInfo>()};
     const ImageOperands operands(ctx, offset, offset2);
+    if (ctx.profile.need_gather_subpixel_offset) {
+        coords = ImageGatherSubpixelOffset(ctx, info, TextureImage(ctx, info, index), coords);
+    }
     return Emit(&EmitContext::OpImageSparseDrefGather, &EmitContext::OpImageDrefGather, ctx, inst,
                 ctx.F32[4], Texture(ctx, info, index), coords, dref, operands.MaskOptional(),
                 operands.Span());