[Flutter GPU] Added support to set primitive type

lib/gpu/lib/src/render_pass.dart

@@ -262,6 +262,11 @@ base class RenderPass extends NativeFieldWrapperClass1 {
     _setCullMode(cullMode.index);
   }
 
+
+  void setPrimitiveType(PrimitiveType primitiveType) {
+    _setPrimitiveType(primitiveType.index);
+}
+
   void setWindingOrder(WindingOrder windingOrder) {
     _setWindingOrder(windingOrder.index);
   }
@@ -421,9 +426,14 @@ base class RenderPass extends NativeFieldWrapperClass1 {
   external void _setCullMode(int cullMode);
 
   @Native<Void Function(Pointer<Void>, Int)>(
+      symbol: 'InternalFlutterGpu_RenderPass_SetPrimitiveType')
+  external void _setPrimitiveType(int primitiveType);
+
+    @Native<Void Function(Pointer<Void>, Int)>(
       symbol: 'InternalFlutterGpu_RenderPass_SetWindingOrder')
   external void _setWindingOrder(int windingOrder);
 
+
   @Native<Bool Function(Pointer<Void>)>(
       symbol: 'InternalFlutterGpu_RenderPass_Draw')
   external bool _draw();

lib/gpu/render_pass.cc

@@ -567,6 +567,15 @@ void InternalFlutterGpu_RenderPass_SetCullMode(
   pipeline_descriptor.SetCullMode(flutter::gpu::ToImpellerCullMode(cull_mode));
 }
 
+void InternalFlutterGpu_RenderPass_SetPrimitiveType(
+    flutter::gpu::RenderPass* wrapper,
+    int primitive_type) {
+  impeller::PipelineDescriptor& pipeline_descriptor =
+      wrapper->GetPipelineDescriptor();
+  pipeline_descriptor.SetPrimitiveType(
+      flutter::gpu::ToImpellerPrimitiveType(primitive_type));
+}
+
 void InternalFlutterGpu_RenderPass_SetWindingOrder(
     flutter::gpu::RenderPass* wrapper,
     int winding_order) {

lib/gpu/render_pass.h

@@ -251,6 +251,11 @@ extern void InternalFlutterGpu_RenderPass_SetCullMode(
     flutter::gpu::RenderPass* wrapper,
     int cull_mode);
 
+FLUTTER_GPU_EXPORT
+extern void InternalFlutterGpu_RenderPass_SetPrimitiveType(
+    flutter::gpu::RenderPass* wrapper,
+    int primitive_type);
+
 FLUTTER_GPU_EXPORT
 extern void InternalFlutterGpu_RenderPass_SetWindingOrder(
     flutter::gpu::RenderPass* wrapper,

testing/dart/gpu_test.dart

@@ -499,4 +499,48 @@ void main() async {
     final ui.Image image = state.renderTexture.asImage();
     await comparer.addGoldenImage(image, 'flutter_gpu_test_cull_mode.png');
   }, skip: !impellerEnabled);
+
+  // Renders a hexagon using line strip primitive type.
+  test('Can render hollow hexagon using line strip primitive type', () async {
+    final state = createSimpleRenderPass();
+
+    final gpu.RenderPipeline pipeline = createUnlitRenderPipeline();
+    state.renderPass.bindPipeline(pipeline);
+
+    // Configure blending with defaults (just to test the bindings).
+    state.renderPass.setColorBlendEnable(true);
+    state.renderPass.setColorBlendEquation(gpu.ColorBlendEquation());
+
+    // Set primitive type
+    state.renderPass.setPrimitiveType(gpu.PrimitiveType.lineStrip);
+
+    final gpu.HostBuffer transients = gpu.gpuContext.createHostBuffer();
+    final gpu.BufferView vertices = transients.emplace(float32(<double>[
+     1.0,  0.0,
+     0.5,  0.8,
+    -0.5,  0.8,
+    -1.0,  0.0,
+    -0.5, -0.8,
+     0.5, -0.8,
+     1.0,  0.0
+    ]));
+    final gpu.BufferView vertInfoData = transients.emplace(float32(<double>[
+      1, 0, 0, 0, // mvp
+      0, 1, 0, 0, // mvp
+      0, 0, 1, 0, // mvp
+      0, 0, 0, 1, // mvp
+      0, 1, 0, 1, // color
+    ]));
+    state.renderPass.bindVertexBuffer(vertices, 7);
+
+    final gpu.UniformSlot vertInfo =
+        pipeline.vertexShader.getUniformSlot('VertInfo');
+    state.renderPass.bindUniform(vertInfo, vertInfoData);
+    state.renderPass.draw();
+
+    state.commandBuffer.submit();
+
+    final ui.Image image = state.renderTexture.asImage();
+    await comparer.addGoldenImage(image, 'flutter_gpu_test_hexgon_line_strip.png');
+  }, skip: !impellerEnabled);
 }