Added support to set viewport (#162602)

Resolves #157201.

Author: AthulJoseph27

engine/src/flutter/lib/gpu/lib/src/render_pass.dart

@@ -168,6 +168,34 @@ base class Scissor {
   }
 }
 
+base class DepthRange {
+  DepthRange({this.zNear = 0.0, this.zFar = 1.0});
+
+  double zNear;
+  double zFar;
+}
+
+base class Viewport {
+  Viewport({
+    this.x = 0,
+    this.y = 0,
+    this.width = 0,
+    this.height = 0,
+    DepthRange? depthRange = null,
+  }) : this.depthRange = depthRange ?? DepthRange();
+
+  int x, y, width, height;
+  DepthRange depthRange;
+
+  void _validate() {
+    if (x < 0 || y < 0 || width < 0 || height < 0) {
+      throw Exception(
+        "Invalid values for viewport. All values should be positive.",
+      );
+    }
+  }
+}
+
 base class RenderTarget {
   const RenderTarget({
     this.colorAttachments = const <ColorAttachment>[],
@@ -346,6 +374,21 @@ base class RenderPass extends NativeFieldWrapperClass1 {
     _setDepthWriteEnable(enable);
   }
 
+  void setViewport(Viewport viewport) {
+    assert(() {
+      viewport._validate();
+      return true;
+    }());
+    _setViewport(
+      viewport.x,
+      viewport.y,
+      viewport.width,
+      viewport.height,
+      viewport.depthRange.zNear,
+      viewport.depthRange.zFar,
+    );
+  }
+
   void setDepthCompareOperation(CompareFunction compareFunction) {
     _setDepthCompareOperation(compareFunction.index);
   }
@@ -508,6 +551,18 @@ base class RenderPass extends NativeFieldWrapperClass1 {
     int lengthInBytes,
   );
 
+  @Native<Void Function(Pointer<Void>, Int, Int, Int, Int, Float, Float)>(
+    symbol: 'InternalFlutterGpu_RenderPass_SetViewport',
+  )
+  external void _setViewport(
+    int x,
+    int y,
+    int width,
+    int height,
+    double depthRangeZNear,
+    double depthRangeZFar,
+  );
+
   @Native<
     Bool Function(
       Pointer<Void>,

engine/src/flutter/lib/gpu/render_pass.cc

@@ -218,6 +218,10 @@ bool RenderPass::Draw() {
 
   render_pass_->SetStencilReference(stencil_reference);
 
+  if (viewport.has_value()) {
+    render_pass_->SetViewport(viewport.value());
+  }
+
   if (scissor.has_value()) {
     render_pass_->SetScissor(scissor.value());
   }
@@ -559,6 +563,27 @@ void InternalFlutterGpu_RenderPass_SetScissor(flutter::gpu::RenderPass* wrapper,
   wrapper->scissor = impeller::TRect<int64_t>::MakeXYWH(x, y, width, height);
 }
 
+void InternalFlutterGpu_RenderPass_SetViewport(
+    flutter::gpu::RenderPass* wrapper,
+    int x,
+    int y,
+    int width,
+    int height,
+    float z_near,
+    float z_far) {
+  auto rect = impeller::TRect<float>::MakeXYWH(x, y, width, height);
+
+  auto depth_range = impeller::DepthRange();
+  depth_range.z_near = z_near;
+  depth_range.z_far = z_far;
+
+  auto viewport = impeller::Viewport();
+  viewport.rect = rect;
+  viewport.depth_range = depth_range;
+
+  wrapper->viewport = viewport;
+}
+
 void InternalFlutterGpu_RenderPass_SetStencilConfig(
     flutter::gpu::RenderPass* wrapper,
     int stencil_compare_operation,

engine/src/flutter/lib/gpu/render_pass.h

@@ -81,6 +81,7 @@ class RenderPass : public RefCountedDartWrappable<RenderPass> {
 
   uint32_t stencil_reference = 0;
   std::optional<impeller::TRect<int64_t>> scissor;
+  std::optional<impeller::Viewport> viewport;
 
   // Helper flag to determine whether the vertex_count should override the
   // element count. The index count takes precedent.
@@ -249,6 +250,16 @@ extern void InternalFlutterGpu_RenderPass_SetScissor(
     int width,
     int height);
 
+FLUTTER_GPU_EXPORT
+extern void InternalFlutterGpu_RenderPass_SetViewport(
+    flutter::gpu::RenderPass* wrapper,
+    int x,
+    int y,
+    int width,
+    int height,
+    float z_near,
+    float z_far);
+
 FLUTTER_GPU_EXPORT
 extern void InternalFlutterGpu_RenderPass_SetCullMode(
     flutter::gpu::RenderPass* wrapper,

engine/src/flutter/testing/dart/gpu_test.dart

@@ -810,4 +810,71 @@ void main() async {
       expect(e.toString(), contains('Invalid values for scissor. All values should be positive.'));
     }
   }, skip: !impellerEnabled);
+
+  test('RenderPass.setViewport doesnt throw for valid values', () async {
+    final state = createSimpleRenderPass();
+
+    state.renderPass.setViewport(gpu.Viewport(x: 25, width: 50, height: 100));
+    state.renderPass.setViewport(gpu.Viewport(width: 50, height: 100));
+  }, skip: !impellerEnabled);
+
+  test('RenderPass.setViewport throws for invalid values', () async {
+    final state = createSimpleRenderPass();
+
+    try {
+      state.renderPass.setViewport(gpu.Viewport(x: -1, width: 50, height: 100));
+      fail('Exception not thrown for invalid viewport.');
+    } catch (e) {
+      expect(e.toString(), contains('Invalid values for viewport. All values should be positive.'));
+    }
+
+    try {
+      state.renderPass.setViewport(gpu.Viewport(width: 50, height: -100));
+      fail('Exception not thrown for invalid viewport.');
+    } catch (e) {
+      expect(e.toString(), contains('Invalid values for viewport. All values should be positive.'));
+    }
+  }, skip: !impellerEnabled);
+
+  // Renders the middle part triangle using viewport.
+  test('Can render portion of the triangle using viewport', () 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.triangle);
+
+    // Set viewport.
+    state.renderPass.setViewport(gpu.Viewport(x: 25, width: 50, height: 100));
+
+    final gpu.HostBuffer transients = gpu.gpuContext.createHostBuffer();
+    final gpu.BufferView vertices = transients.emplace(
+      float32(<double>[-1.0, -1.0, 0.0, 1.0, 1.0, -1.0]),
+    );
+    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, 3);
+
+    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_viewport.png');
+  }, skip: !impellerEnabled);
 }