Add cull mode to command (flutter#13)

Author: bdero

impeller/renderer/backend/metal/formats_mtl.h

@@ -116,6 +116,18 @@ constexpr MTLIndexType ToMTLIndexType(IndexType type) {
   }
 }
 
+constexpr MTLCullMode ToMTLCullMode(CullMode mode) {
+  switch (mode) {
+    case CullMode::kNone:
+      return MTLCullModeNone;
+    case CullMode::kBackFace:
+      return MTLCullModeBack;
+    case CullMode::kFrontFace:
+      return MTLCullModeFront;
+  }
+  return MTLCullModeNone;
+}
+
 constexpr MTLBlendOperation ToMTLBlendOperation(BlendOperation type) {
   switch (type) {
     case BlendOperation::kAdd:

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -426,7 +426,7 @@ static bool Bind(PassBindingsCache& pass,
     [encoder setFrontFacingWinding:command.winding == WindingOrder::kClockwise
                                        ? MTLWindingClockwise
                                        : MTLWindingCounterClockwise];
-    [encoder setCullMode:MTLCullModeNone];
+    [encoder setCullMode:ToMTLCullMode(command.cull_mode)];
     [encoder setStencilReferenceValue:command.stencil_reference];
     if (command.viewport.has_value()) {
       auto v = command.viewport.value();

impeller/renderer/command.h

@@ -70,6 +70,7 @@ struct Command {
   std::string label;
   PrimitiveType primitive_type = PrimitiveType::kTriangle;
   WindingOrder winding = WindingOrder::kClockwise;
+  CullMode cull_mode = CullMode::kNone;
   uint32_t stencil_reference = 0u;
   //----------------------------------------------------------------------------
   /// The viewport coordinates that the rasterizer linearly maps normalized

impeller/renderer/formats.h

@@ -11,9 +11,9 @@
 
 #include "flutter/fml/hash_combine.h"
 #include "flutter/fml/macros.h"
+#include "impeller/geometry/color.h"
 #include "impeller/geometry/rect.h"
 #include "impeller/geometry/scalar.h"
-#include "impeller/geometry/color.h"
 
 namespace impeller {
 
@@ -135,6 +135,12 @@ enum class WindingOrder {
   kCounterClockwise,
 };
 
+enum class CullMode {
+  kNone,
+  kFrontFace,
+  kBackFace,
+};
+
 enum class IndexType {
   kUnknown,
   k16bit,