Revert "[Impeller] Fix MatrixFilter multiplication ordering for subpasses." (#43978)

Reverts #43943

Closes flutter/flutter#131182.
Opens flutter/flutter#130355.

Regression spotted in flutter/flutter#131182

Author: bdero

impeller/aiks/aiks_unittests.cc

@@ -2908,22 +2908,15 @@ TEST_P(AiksTest, DrawPictureWithText) {
 
 TEST_P(AiksTest, MatrixBackdropFilter) {
   Canvas canvas;
-  canvas.DrawPaint({.color = Color::Black()});
-  canvas.SaveLayer({}, std::nullopt);
-  {
-    canvas.DrawCircle(
-        Point(200, 200), 100,
-        {.color = Color::Green(), .blend_mode = BlendMode::kPlus});
-    // Should render a second intersecting circle, offset by 100, 100.
-    canvas.SaveLayer({}, std::nullopt,
-                     [](const FilterInput::Ref& input,
-                        const Matrix& effect_transform, bool is_subpass) {
-                       return FilterContents::MakeMatrixFilter(
-                           input, Matrix::MakeTranslation(Vector2(100, 100)),
-                           {}, Matrix(), true);
-                     });
-    canvas.Restore();
-  }
+  canvas.SaveLayer({}, std::nullopt,
+                   [](const FilterInput::Ref& input,
+                      const Matrix& effect_transform, bool is_subpass) {
+                     return FilterContents::MakeMatrixFilter(
+                         input, Matrix::MakeTranslation(Vector2(100, 100)), {},
+                         Matrix(), true);
+                   });
+  canvas.DrawCircle(Point(100, 100), 100,
+                    {.color = Color::Green(), .blend_mode = BlendMode::kPlus});
   canvas.Restore();
 
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));

impeller/entity/contents/filters/matrix_filter_contents.cc

@@ -34,45 +34,11 @@ std::optional<Entity> MatrixFilterContents::RenderFilter(
     return std::nullopt;
   }
 
-  if (is_subpass_) {
-    // There are two special quirks with how Matrix filters behave when used as
-    // subpass backdrop filters:
-    //
-    // 1. For subpass backdrop filters, the snapshot transform is always just a
-    //    translation that positions the parent pass texture correctly relative
-    //    to the subpass texture. However, this translation always needs to be
-    //    applied in screen space.
-    //
-    //    Since we know the snapshot transform will always have an identity
-    //    basis in this case, we safely reverse the order and apply the filter's
-    //    matrix within the snapshot transform space.
-    //
-    // 2. The filter's matrix needs to be applied within the space defined by
-    //    the scene's current transformation matrix (CTM). For example: If the
-    //    CTM is scaled up, then translations applied by the matrix should be
-    //    magnified accordingly.
-    //
-    //    To accomplish this, we sandwitch the filter's matrix within the CTM in
-    //    both cases. But notice that for the subpass backdrop filter case, we
-    //    use the "effect transform" instead of the Entity's transform!
-    //
-    //    That's because in the subpass backdrop filter case, the Entity's
-    //    transform isn't actually the captured CTM of the scene like it usually
-    //    is; instead, it's just a screen space translation that offsets the
-    //    backdrop texture (as mentioned above). And so we sneak the subpass's
-    //    captured CTM in through the effect transform.
-    //
-
-    snapshot->transform = snapshot->transform *  //
-                          effect_transform *     //
-                          matrix_ *              //
-                          effect_transform.Invert();
-  } else {
-    snapshot->transform = entity.GetTransformation() *           //
-                          matrix_ *                              //
-                          entity.GetTransformation().Invert() *  //
-                          snapshot->transform;
-  }
+  auto& transform = is_subpass_ ? effect_transform : entity.GetTransformation();
+  snapshot->transform = transform *           //
+                        matrix_ *             //
+                        transform.Invert() *  //
+                        snapshot->transform;
   snapshot->sampler_descriptor = sampler_descriptor_;
   return Entity::FromSnapshot(snapshot, entity.GetBlendMode(),
                               entity.GetStencilDepth());

impeller/entity/entity_pass.cc

@@ -465,12 +465,12 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
       return EntityPass::EntityResult::Skip();
     }
 
-    std::shared_ptr<Contents> subpass_backdrop_filter_contents = nullptr;
+    std::shared_ptr<Contents> backdrop_filter_contents = nullptr;
     if (subpass->backdrop_filter_proc_) {
       auto texture = pass_context.GetTexture();
       // Render the backdrop texture before any of the pass elements.
       const auto& proc = subpass->backdrop_filter_proc_;
-      subpass_backdrop_filter_contents =
+      backdrop_filter_contents =
           proc(FilterInput::Make(std::move(texture)), subpass->xformation_,
                /*is_subpass*/ true);
 
@@ -507,10 +507,9 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
       return EntityPass::EntityResult::Skip();
     }
 
-    auto subpass_coverage =
-        (subpass->flood_clip_ || subpass_backdrop_filter_contents)
-            ? coverage_limit
-            : GetSubpassCoverage(*subpass, coverage_limit);
+    auto subpass_coverage = (subpass->flood_clip_ || backdrop_filter_contents)
+                                ? coverage_limit
+                                : GetSubpassCoverage(*subpass, coverage_limit);
     if (!subpass_coverage.has_value()) {
       return EntityPass::EntityResult::Skip();
     }
@@ -533,18 +532,17 @@ EntityPass::EntityResult EntityPass::GetEntityForElement(
 
     // Stencil textures aren't shared between EntityPasses (as much of the
     // time they are transient).
-    if (!subpass->OnRender(
-            renderer,                  // renderer
-            root_pass_size,            // root_pass_size
-            subpass_target,            // pass_target
-            subpass_coverage->origin,  // global_pass_position
-            subpass_coverage->origin -
-                global_pass_position,         // local_pass_position
-            ++pass_depth,                     // pass_depth
-            stencil_coverage_stack,           // stencil_coverage_stack
-            subpass->stencil_depth_,          // stencil_depth_floor
-            subpass_backdrop_filter_contents  // backdrop_filter_contents
-            )) {
+    if (!subpass->OnRender(renderer,                  // renderer
+                           root_pass_size,            // root_pass_size
+                           subpass_target,            // pass_target
+                           subpass_coverage->origin,  // global_pass_position
+                           subpass_coverage->origin -
+                               global_pass_position,  // local_pass_position
+                           ++pass_depth,              // pass_depth
+                           stencil_coverage_stack,    // stencil_coverage_stack
+                           subpass->stencil_depth_,   // stencil_depth_floor
+                           backdrop_filter_contents  // backdrop_filter_contents
+                           )) {
       // Validation error messages are triggered for all `OnRender()` failure
       // cases.
       return EntityPass::EntityResult::Failure();