[Impeller] Add PolygonMode to render layer (#39810)

Author: bdero

impeller/renderer/backend/gles/render_pass_gles.cc

@@ -408,11 +408,22 @@ struct RenderPassData {
       return false;
     }
 
+    //--------------------------------------------------------------------------
+    /// Determine the primitive type.
+    ///
+    // GLES doesn't support setting the fill mode, so override the primitive
+    // with GL_LINE_STRIP to somewhat emulate PolygonMode::kLine. This isn't
+    // correct; full triangle outlines won't be drawn and disconnected
+    // geometry may appear connected. However this can still be useful for
+    // wireframe debug views.
+    auto mode = pipeline.GetDescriptor().GetPolygonMode() == PolygonMode::kLine
+                    ? GL_LINE_STRIP
+                    : ToMode(pipeline.GetDescriptor().GetPrimitiveType());
+
     //--------------------------------------------------------------------------
     /// Finally! Invoke the draw call.
     ///
-    PrimitiveType primitive_type = pipeline.GetDescriptor().GetPrimitiveType();
-    gl.DrawElements(ToMode(primitive_type),           // mode
+    gl.DrawElements(mode,                             // mode
                     command.index_count,              // count
                     ToIndexType(command.index_type),  // type
                     reinterpret_cast<const GLvoid*>(static_cast<GLsizei>(

impeller/renderer/backend/metal/formats_mtl.h

@@ -150,6 +150,16 @@ constexpr MTLPrimitiveType ToMTLPrimitiveType(PrimitiveType type) {
   return MTLPrimitiveTypePoint;
 }
 
+constexpr MTLTriangleFillMode ToMTLTriangleFillMode(PolygonMode mode) {
+  switch (mode) {
+    case PolygonMode::kFill:
+      return MTLTriangleFillModeFill;
+    case PolygonMode::kLine:
+      return MTLTriangleFillModeLines;
+  }
+  return MTLTriangleFillModeFill;
+}
+
 constexpr MTLIndexType ToMTLIndexType(IndexType type) {
   switch (type) {
     case IndexType::k16bit:

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -468,6 +468,8 @@ static bool Bind(PassBindingsCache& pass,
                                        ? MTLWindingClockwise
                                        : MTLWindingCounterClockwise];
     [encoder setCullMode:ToMTLCullMode(pipeline_desc.GetCullMode())];
+    [encoder setTriangleFillMode:ToMTLTriangleFillMode(
+                                     pipeline_desc.GetPolygonMode())];
     [encoder setStencilReferenceValue:command.stencil_reference];
 
     if (!bind_stage_resources(command.vertex_bindings, ShaderStage::kVertex)) {

impeller/renderer/backend/vulkan/formats_vk.h

@@ -336,6 +336,16 @@ constexpr vk::IndexType ToVKIndexType(IndexType index_type) {
   FML_UNREACHABLE();
 }
 
+constexpr vk::PolygonMode ToVKPolygonMode(PolygonMode mode) {
+  switch (mode) {
+    case PolygonMode::kFill:
+      return vk::PolygonMode::eFill;
+    case PolygonMode::kLine:
+      return vk::PolygonMode::eLine;
+  }
+  FML_UNREACHABLE();
+}
+
 constexpr vk::PrimitiveTopology ToVKPrimitiveTopology(PrimitiveType primitive) {
   switch (primitive) {
     case PrimitiveType::kTriangle:

impeller/renderer/backend/vulkan/pipeline_library_vk.cc

@@ -275,7 +275,7 @@ std::unique_ptr<PipelineCreateInfoVK> PipelineLibraryVK::CreatePipeline(
   vk::PipelineRasterizationStateCreateInfo rasterization_state;
   rasterization_state.setFrontFace(vk::FrontFace::eClockwise);
   rasterization_state.setCullMode(vk::CullModeFlagBits::eNone);
-  rasterization_state.setPolygonMode(vk::PolygonMode::eFill);
+  rasterization_state.setPolygonMode(ToVKPolygonMode(desc.GetPolygonMode()));
   // requires GPU extensions to change.
   {
     rasterization_state.setLineWidth(1.0f);

impeller/renderer/formats.h

@@ -215,6 +215,11 @@ enum class PrimitiveType {
   // checks. Hence, they are not supported here.
 };
 
+enum class PolygonMode {
+  kFill,
+  kLine,
+};
+
 struct DepthRange {
   Scalar z_near = 0.0;
   Scalar z_far = 1.0;

impeller/renderer/pipeline_descriptor.cc

@@ -41,6 +41,7 @@ std::size_t PipelineDescriptor::GetHash() const {
   fml::HashCombineSeed(seed, winding_order_);
   fml::HashCombineSeed(seed, cull_mode_);
   fml::HashCombineSeed(seed, primitive_type_);
+  fml::HashCombineSeed(seed, polygon_mode_);
   return seed;
 }
 
@@ -59,7 +60,8 @@ bool PipelineDescriptor::IsEqual(const PipelineDescriptor& other) const {
              other.back_stencil_attachment_descriptor_ &&
          winding_order_ == other.winding_order_ &&
          cull_mode_ == other.cull_mode_ &&
-         primitive_type_ == other.primitive_type_;
+         primitive_type_ == other.primitive_type_ &&
+         polygon_mode_ == other.polygon_mode_;
 }
 
 PipelineDescriptor& PipelineDescriptor::SetLabel(std::string label) {
@@ -259,4 +261,12 @@ PrimitiveType PipelineDescriptor::GetPrimitiveType() const {
   return primitive_type_;
 }
 
+void PipelineDescriptor::SetPolygonMode(PolygonMode mode) {
+  polygon_mode_ = mode;
+}
+
+PolygonMode PipelineDescriptor::GetPolygonMode() const {
+  return polygon_mode_;
+}
+
 }  // namespace impeller

impeller/renderer/pipeline_descriptor.h

@@ -125,6 +125,10 @@ class PipelineDescriptor final : public Comparable<PipelineDescriptor> {
 
   PrimitiveType GetPrimitiveType() const;
 
+  void SetPolygonMode(PolygonMode mode);
+
+  PolygonMode GetPolygonMode() const;
+
  private:
   std::string label_;
   SampleCount sample_count_ = SampleCount::kCount1;
@@ -142,6 +146,7 @@ class PipelineDescriptor final : public Comparable<PipelineDescriptor> {
   std::optional<StencilAttachmentDescriptor>
       back_stencil_attachment_descriptor_;
   PrimitiveType primitive_type_ = PrimitiveType::kTriangle;
+  PolygonMode polygon_mode_ = PolygonMode::kFill;
 };
 
 }  // namespace impeller

impeller/renderer/renderer_unittests.cc

@@ -54,9 +54,6 @@ TEST_P(RendererTest, CanCreateBoxPrimitive) {
   auto desc = BoxPipelineBuilder::MakeDefaultPipelineDescriptor(*context);
   ASSERT_TRUE(desc.has_value());
   desc->SetSampleCount(SampleCount::kCount4);
-  auto box_pipeline =
-      context->GetPipelineLibrary()->GetPipeline(std::move(desc)).Get();
-  ASSERT_TRUE(box_pipeline);
 
   // Vertex buffer.
   VertexBufferBuilder<VS::PerVertexData> vertex_builder;
@@ -79,9 +76,19 @@ TEST_P(RendererTest, CanCreateBoxPrimitive) {
   auto sampler = context->GetSamplerLibrary()->GetSampler({});
   ASSERT_TRUE(sampler);
   SinglePassCallback callback = [&](RenderPass& pass) {
+    ImGui::Begin("Controls", nullptr, ImGuiWindowFlags_AlwaysAutoResize);
+    static bool wireframe;
+    ImGui::Checkbox("Wireframe", &wireframe);
+    ImGui::End();
+
+    desc->SetPolygonMode(wireframe ? PolygonMode::kLine : PolygonMode::kFill);
+    auto pipeline = context->GetPipelineLibrary()->GetPipeline(desc).Get();
+
+    assert(pipeline && pipeline->IsValid());
+
     Command cmd;
     cmd.label = "Box";
-    cmd.pipeline = box_pipeline;
+    cmd.pipeline = pipeline;
 
     cmd.BindVertices(vertex_buffer);