Stub Maxwell3D Alpha Testing

We stub alpha testing as it doesn't exist in Vulkan and few titles use it, it can be emulated in the future using a shader patch with manually discarding fragments failing the alpha test function but this'll be added in later as it isn't high priority at the moment and has associated overhead with it so other options might be explored at the time.

app/src/main/cpp/skyline/gpu/interconnect/graphics_context.h

@@ -531,5 +531,10 @@ namespace skyline::gpu::interconnect {
                 }
             }();
         }
+
+        void SetAlphaTestEnable(bool enable) {
+            if (enable)
+                Logger::Warn("Cannot enable alpha testing due to Vulkan constraints");
+        }
     };
 }

app/src/main/cpp/skyline/soc/gm20b/engines/maxwell_3d.cpp

@@ -183,6 +183,10 @@ namespace skyline::soc::gm20b::engine::maxwell3d {
                     context.UpdateRenderTargetControl(renderTargetControl);
                 })
 
+                MAXWELL3D_CASE(alphaTestEnable, {
+                    context.SetAlphaTestEnable(alphaTestEnable);
+                })
+
                 MAXWELL3D_CASE(lineWidthSmooth, {
                     if (*registers.lineSmoothEnable)
                         context.SetLineWidth(lineWidthSmooth);

app/src/main/cpp/skyline/soc/gm20b/engines/maxwell_3d.h

@@ -108,6 +108,7 @@ namespace skyline::soc::gm20b::engine::maxwell3d {
             Register<0x3EB, u32> rtSeparateFragData;
             Register<0x458, std::array<type::VertexAttribute, 0x20>> vertexAttributeState;
             Register<0x487, type::RenderTargetControl> renderTargetControl;
+            Register<0x4BB, u32> alphaTestEnable;
             Register<0x4C3, type::CompareOp> depthTestFunc;
             Register<0x4C4, float> alphaTestRef;
             Register<0x4C5, type::CompareOp> alphaTestFunc;