[GPU] Primitive processor with Vulkan 1.0 base cases, 24-bit indices and clamping

src/xenia/gpu/draw_util.h

@@ -34,6 +34,50 @@ namespace draw_util {
 // for use with the top-left rasterization rule later.
 int32_t FloatToD3D11Fixed16p8(float f32);
 
+// Polygonal primitive types (not including points and lines) are rasterized as
+// triangles, have front and back faces, and also support face culling and fill
+// modes (polymode_front_ptype, polymode_back_ptype). Other primitive types are
+// always "front" (but don't support front face and back face culling, according
+// to OpenGL and Vulkan specifications - even if glCullFace is
+// GL_FRONT_AND_BACK, points and lines are still drawn), and may in some cases
+// use the "para" registers instead of "front" or "back" (for "parallelogram" -
+// like poly_offset_para_enable).
+constexpr bool IsPrimitivePolygonal(bool vgt_output_path_is_tessellation_enable,
+                                    xenos::PrimitiveType type) {
+  if (vgt_output_path_is_tessellation_enable &&
+      (type == xenos::PrimitiveType::kTrianglePatch ||
+       type == xenos::PrimitiveType::kQuadPatch)) {
+    // For patch primitive types, the major mode is always explicit, so just
+    // checking if VGT_OUTPUT_PATH_CNTL::path_select is kTessellationEnable is
+    // enough.
+    return true;
+  }
+  switch (type) {
+    case xenos::PrimitiveType::kTriangleList:
+    case xenos::PrimitiveType::kTriangleFan:
+    case xenos::PrimitiveType::kTriangleStrip:
+    case xenos::PrimitiveType::kTriangleWithWFlags:
+    case xenos::PrimitiveType::kQuadList:
+    case xenos::PrimitiveType::kQuadStrip:
+    case xenos::PrimitiveType::kPolygon:
+      return true;
+    default:
+      break;
+  }
+  // TODO(Triang3l): Investigate how kRectangleList should be treated - possibly
+  // actually drawn as two polygons on the console, however, the current
+  // geometry shader doesn't care about the winding order - allowing backface
+  // culling for rectangles currently breaks Gears of War 2.
+  return false;
+}
+
+inline bool IsPrimitivePolygonal(const RegisterFile& regs) {
+  return IsPrimitivePolygonal(
+      regs.Get<reg::VGT_OUTPUT_PATH_CNTL>().path_select ==
+          xenos::VGTOutputPath::kTessellationEnable,
+      regs.Get<reg::VGT_DRAW_INITIATOR>().prim_type);
+}
+
 // Whether with the current state, any samples to rasterize (for any reason, not
 // only to write something to a render target, but also to do sample counting or
 // pixel shader memexport) can be generated. Finally dropping draw calls can