[Impeller] Assign subpass depth on restore rather than creation. (flutter/engine#50626)

The subpass depth is used for drawing the texture to the parent pass. So it needs a depth > all of the clips contained within the subpass.

Also correct the way we're assigning the depth value in shaders.

engine/src/flutter/impeller/aiks/aiks_unittests.cc

@@ -3525,10 +3525,10 @@ TEST_P(AiksTest, CorrectClipDepthAssignedToEntities) {
   canvas.DrawRRect(Rect::MakeLTRB(0, 0, 100, 100), {10, 10}, {});  // Depth 2
   canvas.Save();
   {
-    canvas.ClipRRect(Rect::MakeLTRB(0, 0, 50, 50), {10, 10}, {});  // Depth 5
-    canvas.SaveLayer({});                                          // Depth 3
+    canvas.ClipRRect(Rect::MakeLTRB(0, 0, 50, 50), {10, 10}, {});  // Depth 4
+    canvas.SaveLayer({});                                          // Depth 4
     {
-      canvas.DrawRRect(Rect::MakeLTRB(0, 0, 50, 50), {10, 10}, {});  // Depth 4
+      canvas.DrawRRect(Rect::MakeLTRB(0, 0, 50, 50), {10, 10}, {});  // Depth 3
     }
     canvas.Restore();  // Restore the savelayer.
   }
@@ -3538,9 +3538,13 @@ TEST_P(AiksTest, CorrectClipDepthAssignedToEntities) {
   auto picture = canvas.EndRecordingAsPicture();
   std::array<uint32_t, 5> expected = {
       2,  // DrawRRect
-      4,  // ClipRRect
-      3,  // SaveLayer
-      4,  // DrawRRect
+      4,  // ClipRRect -- Has a depth value equal to the max depth of all the
+          //              content it affect. In this case, the SaveLayer and all
+          //              its contents are affected.
+      4,  // SaveLayer -- The SaveLayer is drawn to the parent pass after its
+          //              contents are rendered, so it should have a depth value
+          //              greater than all its contents.
+      3,  // DrawRRect
       5,  // Restore (will be removed once we switch to the clip depth approach)
   };
   std::vector<uint32_t> actual;
@@ -3557,7 +3561,7 @@ TEST_P(AiksTest, CorrectClipDepthAssignedToEntities) {
 
   ASSERT_EQ(actual.size(), expected.size());
   for (size_t i = 0; i < expected.size(); i++) {
-    EXPECT_EQ(actual[i], expected[i]) << "Index: " << i;
+    EXPECT_EQ(expected[i], actual[i]) << "Index: " << i;
   }
 }
 

engine/src/flutter/impeller/aiks/canvas.cc

@@ -176,7 +176,6 @@ void Canvas::Save(bool create_subpass,
   if (create_subpass) {
     entry.rendering_mode = Entity::RenderingMode::kSubpass;
     auto subpass = std::make_unique<EntityPass>();
-    subpass->SetNewClipDepth(++current_depth_);
     subpass->SetEnableOffscreenCheckerboard(
         debug_options.offscreen_texture_checkerboard);
     if (backdrop_filter) {
@@ -214,6 +213,7 @@ bool Canvas::Restore() {
 
   if (transform_stack_.back().rendering_mode ==
       Entity::RenderingMode::kSubpass) {
+    current_pass_->SetNewClipDepth(++current_depth_);
     current_pass_ = GetCurrentPass().GetSuperpass();
     FML_DCHECK(current_pass_);
   }

engine/src/flutter/impeller/entity/contents/clip_contents.cc

@@ -200,6 +200,7 @@ bool ClipRestoreContents::Render(const ContentContext& renderer,
       vtx_builder.CreateVertexBuffer(renderer.GetTransientsBuffer()));
 
   VS::FrameInfo info;
+  info.depth = entity.GetShaderClipDepth();
   info.mvp = pass.GetOrthographicTransform();
   VS::BindFrameInfo(pass, renderer.GetTransientsBuffer().EmplaceUniform(info));
 

engine/src/flutter/impeller/entity/contents/contents.cc

@@ -21,7 +21,12 @@ ContentContextOptions OptionsFromPass(const RenderPass& pass) {
   ContentContextOptions opts;
   opts.sample_count = pass.GetSampleCount();
   opts.color_attachment_pixel_format = pass.GetRenderTargetPixelFormat();
-  opts.has_depth_stencil_attachments = pass.HasStencilAttachment();
+
+  bool has_depth_stencil_attachments =
+      pass.HasDepthAttachment() && pass.HasStencilAttachment();
+  FML_DCHECK(pass.HasDepthAttachment() == pass.HasStencilAttachment());
+
+  opts.has_depth_stencil_attachments = has_depth_stencil_attachments;
   return opts;
 }
 

engine/src/flutter/impeller/entity/contents/filters/blend_filter_contents.cc

@@ -470,6 +470,7 @@ std::optional<Entity> BlendFilterContents::CreateForegroundPorterDuffBlend(
 
     FS::FragInfo frag_info;
     VS::FrameInfo frame_info;
+    frame_info.depth = entity.GetShaderClipDepth();
 
     auto dst_sampler_descriptor = dst_snapshot->sampler_descriptor;
     if (renderer.GetDeviceCapabilities().SupportsDecalSamplerAddressMode()) {

engine/src/flutter/impeller/entity/contents/filters/gaussian_blur_filter_contents.cc

@@ -89,6 +89,7 @@ fml::StatusOr<RenderTarget> MakeDownsampleSubpass(
         pass.SetPipeline(renderer.GetTexturePipeline(pipeline_options));
 
         TextureFillVertexShader::FrameInfo frame_info;
+        frame_info.depth = 0.0;
         frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
         frame_info.texture_sampler_y_coord_scale = 1.0;
         frame_info.alpha = 1.0;

engine/src/flutter/impeller/entity/shaders/blending/framebuffer_blend.vert

@@ -21,7 +21,8 @@ in vec2 src_texture_coords;
 out vec2 v_src_texture_coords;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(vertices, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(vertices, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_src_texture_coords =
       IPRemapCoords(src_texture_coords, frame_info.src_y_coord_scale);
 }

engine/src/flutter/impeller/entity/shaders/blending/porter_duff_blend.vert

@@ -20,7 +20,8 @@ out vec2 v_texture_coords;
 out f16vec4 v_color;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(vertices, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(vertices, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_color = f16vec4(color);
   v_texture_coords =
       IPRemapCoords(texture_coords, frame_info.texture_sampler_y_coord_scale);

engine/src/flutter/impeller/entity/shaders/clip.vert

@@ -13,5 +13,6 @@ frame_info;
 in vec2 position;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
 }

engine/src/flutter/impeller/entity/shaders/glyph_atlas.vert

@@ -80,7 +80,8 @@ void main() {
                     0.0, 1.0);
   }
 
-  gl_Position = frame_info.mvp * vec4(position.xy, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position.xy, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_uv = uv_origin + unit_position * uv_size;
   v_text_color = frame_info.text_color;
 }

engine/src/flutter/impeller/entity/shaders/gradient_fill.vert

@@ -17,6 +17,7 @@ in vec2 position;
 out vec2 v_position;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_position = IPVec2TransformPosition(frame_info.matrix, position);
 }

engine/src/flutter/impeller/entity/shaders/position_color.vert

@@ -17,6 +17,7 @@ in vec4 color;
 out f16vec4 v_color;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_color = f16vec4(color);
 }

engine/src/flutter/impeller/entity/shaders/rrect_blur.vert

@@ -15,7 +15,8 @@ in vec2 position;
 out vec2 v_position;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   // The fragment stage uses local coordinates to compute the blur.
   v_position = position;
 }

engine/src/flutter/impeller/entity/shaders/runtime_effect.vert

@@ -17,6 +17,7 @@ in vec2 position;
 out vec2 _fragCoord;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   _fragCoord = position;
 }

engine/src/flutter/impeller/entity/shaders/solid_fill.vert

@@ -17,5 +17,6 @@ IMPELLER_MAYBE_FLAT out f16vec4 v_color;
 
 void main() {
   v_color = frame_info.color;
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
 }

engine/src/flutter/impeller/entity/shaders/texture_fill.vert

@@ -20,7 +20,8 @@ out vec2 v_texture_coords;
 IMPELLER_MAYBE_FLAT out float16_t v_alpha;
 
 void main() {
-  gl_Position = frame_info.mvp * vec4(position, frame_info.depth, 1.0);
+  gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
+  gl_Position.z = frame_info.depth;
   v_alpha = frame_info.alpha;
   v_texture_coords =
       IPRemapCoords(texture_coords, frame_info.texture_sampler_y_coord_scale);

engine/src/flutter/impeller/renderer/compute_subgroup_unittests.cc

@@ -159,6 +159,7 @@ TEST_P(ComputeSubgroupTest, PathPlayground) {
                      .index_type = IndexType::kNone});
 
     VS::FrameInfo frame_info;
+    frame_info.depth = 0.0;
     auto world_matrix = Matrix::MakeScale(GetContentScale());
     frame_info.mvp = pass.GetOrthographicTransform() * world_matrix;
     frame_info.color = Color::Red().Premultiply();
@@ -357,6 +358,7 @@ TEST_P(ComputeSubgroupTest, LargePath) {
                      .index_type = IndexType::kNone});
 
     VS::FrameInfo frame_info;
+    frame_info.depth = 0.0;
     auto world_matrix = Matrix::MakeScale(GetContentScale());
     frame_info.mvp = pass.GetOrthographicTransform() * world_matrix;
     frame_info.color = Color::Red().Premultiply();
@@ -436,6 +438,7 @@ TEST_P(ComputeSubgroupTest, QuadAndCubicInOnePath) {
                      .index_type = IndexType::kNone});
 
     VS::FrameInfo frame_info;
+    frame_info.depth = 0.0;
     auto world_matrix = Matrix::MakeScale(GetContentScale());
     frame_info.mvp = pass.GetOrthographicTransform() * world_matrix;
     frame_info.color = Color::Red().Premultiply();

engine/src/flutter/impeller/renderer/render_pass.cc

@@ -12,6 +12,7 @@ RenderPass::RenderPass(std::shared_ptr<const Context> context,
     : context_(std::move(context)),
       sample_count_(target.GetSampleCount()),
       pixel_format_(target.GetRenderTargetPixelFormat()),
+      has_depth_attachment_(target.GetDepthAttachment().has_value()),
       has_stencil_attachment_(target.GetStencilAttachment().has_value()),
       render_target_size_(target.GetRenderTargetSize()),
       render_target_(target),
@@ -27,6 +28,10 @@ PixelFormat RenderPass::GetRenderTargetPixelFormat() const {
   return pixel_format_;
 }
 
+bool RenderPass::HasDepthAttachment() const {
+  return has_depth_attachment_;
+}
+
 bool RenderPass::HasStencilAttachment() const {
   return has_stencil_attachment_;
 }

engine/src/flutter/impeller/renderer/render_pass.h

@@ -156,6 +156,10 @@ class RenderPass : public ResourceBinder {
   /// @brief      The pixel format of the attached render target.
   PixelFormat GetRenderTargetPixelFormat() const;
 
+  //----------------------------------------------------------------------------
+  /// @brief      Whether the render target has a depth attachment.
+  bool HasDepthAttachment() const;
+
   //----------------------------------------------------------------------------
   /// @brief      Whether the render target has an stencil attachment.
   bool HasStencilAttachment() const;
@@ -169,6 +173,7 @@ class RenderPass : public ResourceBinder {
   // a const reference.
   const SampleCount sample_count_;
   const PixelFormat pixel_format_;
+  const bool has_depth_attachment_;
   const bool has_stencil_attachment_;
   const ISize render_target_size_;
   const RenderTarget render_target_;