GS/HW: Fix flat shaded color in AA1 shader.

bin/resources/shaders/dx11/tfx.fx

@@ -1729,6 +1729,11 @@ VS_OUTPUT vs_main_expand(uint vid : SV_VertexID)
 		}
 
 		vtx.interior = 0;
+
+		#if !VS_IIP
+			// Get the provoking vertex color (first vertex in DX)
+			vtx.c = i0 == 0 ? vtx.c : (i1 == 0 ? other.c : opposite.c);
+		#endif
 	}
 
 	return vtx;

bin/resources/shaders/opengl/tfx_vgs.glsl

@@ -308,6 +308,11 @@ void main()
 		}
 
 		VSout.interior = 0;
+
+		#if !VS_IIP
+			// Get the provoking vertex color (last vertex in GL)
+			vtx.c = i0 == 2 ? vtx.c : (i1 == 2 ? other.c : opposite.c);
+		#endif
 	}
 
 #endif

bin/resources/shaders/vulkan/tfx.glsl

@@ -316,6 +316,11 @@ void main()
 		}
 
 		vsOut.interior = 0;
+
+		#if !VS_IIP
+			// Get the provoking vertex color (last vertex in VK)
+			vtx.c = i0 == 2 ? vtx.c : (i1 == 2 ? other.c : opposite.c);
+		#endif
 	}
 
 #endif

pcsx2/GS/Renderers/Metal/tfx.metal

@@ -396,6 +396,12 @@ vertex MainVSOut vs_main_expand(
 				}
 
 				out.interior = 0;
+
+				if (NOT_IIP)
+				{
+					// Get the provoking vertex color (first vertex in Metal)
+					out.fc = i0 == 0 ? out.fc : (i1 == 0 ? other.fc : opposite.fc);
+				}
 			}
 
 			return out;

pcsx2/ShaderCacheVersion.h

@@ -3,4 +3,4 @@
 
 /// Version number for GS and other shaders. Increment whenever any of the contents of the
 /// shaders change, to invalidate the cache.
-static constexpr u32 SHADER_CACHE_VERSION = 92; // Last changed in PR 14399
+static constexpr u32 SHADER_CACHE_VERSION = 93; // Last changed in PR 14435