Pica/CommandProcessor: Workaround games not setting the input position's w component.

src/video_core/command_processor.cpp

@@ -112,6 +112,10 @@ static inline void WritePicaReg(u32 id, u32 value, u32 mask) {
                 // Initialize data for the current vertex
                 VertexShader::InputVertex input;
 
+                // Load a debugging token to check whether this gets loaded by the running
+                // application or not.
+                input.attr[0].w = float24::FromRawFloat24(0x00abcdef);
+
                 for (int i = 0; i < attribute_config.GetNumTotalAttributes(); ++i) {
                     for (unsigned int comp = 0; comp < vertex_attribute_elements[i]; ++comp) {
                         const u8* srcdata = Memory::GetPointer(PAddrToVAddr(vertex_attribute_sources[i] + vertex_attribute_strides[i] * vertex + comp * vertex_attribute_element_size[i]));
@@ -136,6 +140,16 @@ static inline void WritePicaReg(u32 id, u32 value, u32 mask) {
                     }
                 }
 
+                // HACK: Some games do not initialize the vertex position's w component. This leads
+                //       to critical issues since it messes up perspective division. As a
+                //       workaround, we force the fourth component to 1.0 if we find this to be the
+                //       case.
+                //       To do this, we additionally have to assume that the first input attribute
+                //       is the vertex position, since there's no information about this other than
+                //       the empiric observation that this is usually the case.
+                if (input.attr[0].w == float24::FromRawFloat24(0x00abcdef))
+                    input.attr[0].w = float24::FromFloat32(1.0);
+
                 if (g_debug_context)
                     g_debug_context->OnEvent(DebugContext::Event::VertexLoaded, (void*)&input);