GPU: Flip the triangle front face winding if the GPU is configured to not flip the triangles.

OpenGL's default behavior is already correct when the GPU is configured to flip the triangles.

This fixes 1-2 Switch's splash screen.

src/video_core/engines/maxwell_3d.h

@@ -478,7 +478,9 @@ public:
 
                 u32 depth_write_enabled;
 
-                INSERT_PADDING_WORDS(0x8);
+                INSERT_PADDING_WORDS(0x7);
+
+                u32 d3d_cull_mode;
 
                 BitField<0, 3, ComparisonOp> depth_test_func;
 
@@ -498,7 +500,13 @@ public:
                     u32 enable[NumRenderTargets];
                 } blend;
 
-                INSERT_PADDING_WORDS(0x2D);
+                INSERT_PADDING_WORDS(0xB);
+
+                union {
+                    BitField<4, 1, u32> triangle_rast_flip;
+                } screen_y_control;
+
+                INSERT_PADDING_WORDS(0x21);
 
                 u32 vb_element_base;
 
@@ -528,7 +536,12 @@ public:
                     }
                 } tic;
 
-                INSERT_PADDING_WORDS(0x22);
+                INSERT_PADDING_WORDS(0x21);
+
+                union {
+                    BitField<2, 1, u32> coord_origin;
+                    BitField<3, 10, u32> enable;
+                } point_coord_replace;
 
                 struct {
                     u32 code_address_high;
@@ -818,11 +831,14 @@ ASSERT_REG_POSITION(rt_control, 0x487);
 ASSERT_REG_POSITION(depth_test_enable, 0x4B3);
 ASSERT_REG_POSITION(independent_blend_enable, 0x4B9);
 ASSERT_REG_POSITION(depth_write_enabled, 0x4BA);
+ASSERT_REG_POSITION(d3d_cull_mode, 0x4C2);
 ASSERT_REG_POSITION(depth_test_func, 0x4C3);
 ASSERT_REG_POSITION(blend, 0x4CF);
+ASSERT_REG_POSITION(screen_y_control, 0x4EB);
 ASSERT_REG_POSITION(vb_element_base, 0x50D);
 ASSERT_REG_POSITION(tsc, 0x557);
 ASSERT_REG_POSITION(tic, 0x55D);
+ASSERT_REG_POSITION(point_coord_replace, 0x581);
 ASSERT_REG_POSITION(code_address, 0x582);
 ASSERT_REG_POSITION(draw, 0x585);
 ASSERT_REG_POSITION(index_array, 0x5F2);

src/video_core/renderer_opengl/gl_rasterizer.cpp

@@ -771,6 +771,16 @@ void RasterizerOpenGL::SyncCullMode() {
     if (state.cull.enabled) {
         state.cull.front_face = MaxwellToGL::FrontFace(regs.cull.front_face);
         state.cull.mode = MaxwellToGL::CullFace(regs.cull.cull_face);
+
+        // If the GPU is configured to flip the rasterized triangles, then we need to flip the
+        // notion of front and back. Note: We flip the triangles when the value of the register is 0
+        // because OpenGL already does it for us.
+        if (regs.screen_y_control.triangle_rast_flip == 0) {
+            if (state.cull.front_face == GL_CCW)
+                state.cull.front_face = GL_CW;
+            else if (state.cull.front_face == GL_CW)
+                state.cull.front_face = GL_CCW;
+        }
     }
 }