Don't populate colour targets with an empty write mask

Avoids breaking VK spec in BOTW, as it has the same colour attachment bound twice, but the former is masked out entirely.

app/src/main/cpp/skyline/gpu/interconnect/maxwell_3d/pipeline_state.cpp

@@ -300,6 +300,7 @@ namespace skyline::gpu::interconnect::maxwell3d {
     void ColorBlendState::Flush(PackedPipelineState &packedState) {
         packedState.logicOpEnable = engine->logicOp.enable;
         packedState.SetLogicOp(engine->logicOp.func);
+        writtenCtMask.reset();
 
         for (u32 i{}; i < engine::ColorTargetCount; i++) {
             auto ctWrite{[&]() {
@@ -315,6 +316,8 @@ namespace skyline::gpu::interconnect::maxwell3d {
                 packedState.SetAttachmentBlendState(i, enable, ctWrite, engine->blendPerTargets[i]);
             else
                 packedState.SetAttachmentBlendState(i, enable, ctWrite, engine->blend);
+
+            writtenCtMask.set(i, ctWrite.Any());
         }
     }
 
@@ -392,10 +395,12 @@ namespace skyline::gpu::interconnect::maxwell3d {
             shaderBinaries[i] = stage.binary;
         }
 
+        colorBlend.Update(packedState);
+
         colorAttachments.clear();
         packedState.colorRenderTargetFormats = {};
         for (size_t i{}; i < engine::ColorTargetCount; i++) {
-            if (i < ctSelect.count) {
+            if (i < ctSelect.count && colorBlend.Get().writtenCtMask.test(i)) {
                 const auto &rt{colorRenderTargets[ctSelect[i]].UpdateGet(ctx, packedState)};
                 const auto view{rt.view.get()};
                 packedState.SetColorRenderTargetFormat(ctSelect[i], rt.format);
@@ -417,7 +422,6 @@ namespace skyline::gpu::interconnect::maxwell3d {
         tessellation.Update(packedState);
         rasterization.Update(packedState);
         depthStencil.Update(packedState);
-        colorBlend.Update(packedState);
         transformFeedback.Update(packedState);
         globalShaderConfig.Update(packedState);
 

app/src/main/cpp/skyline/gpu/interconnect/maxwell_3d/pipeline_state.h

@@ -234,6 +234,8 @@ namespace skyline::gpu::interconnect::maxwell3d {
         dirty::BoundSubresource<EngineRegisters> engine;
 
       public:
+        std::bitset<engine::ColorTargetCount> writtenCtMask{};
+
         ColorBlendState(dirty::Handle dirtyHandle, DirtyManager &manager, const EngineRegisters &engine);
 
         void Flush(PackedPipelineState &packedState);

app/src/main/cpp/skyline/soc/gm20b/engines/maxwell/types.h

@@ -718,6 +718,10 @@ namespace skyline::soc::gm20b::engine::maxwell3d::type {
     static_assert(sizeof(ViewportClipControl) == sizeof(u32));
 
     union CtWrite {
+        bool Any() const {
+            return rEnable || gEnable || bEnable || aEnable;
+        }
+
         u32 raw;
 
         struct {