Reland elevation test (#8633)

Reland "Add a unit test for PhysicalShapeLayer (#8616)"

This reverts commit 91b71070.

The only change is the namespace.

ci/licenses_golden/licenses_flutter

@@ -89,6 +89,7 @@ FILE: ../../../flutter/flow/layers/performance_overlay_layer.h
 FILE: ../../../flutter/flow/layers/performance_overlay_layer_unittests.cc
 FILE: ../../../flutter/flow/layers/physical_shape_layer.cc
 FILE: ../../../flutter/flow/layers/physical_shape_layer.h
+FILE: ../../../flutter/flow/layers/physical_shape_layer_unittests.cc
 FILE: ../../../flutter/flow/layers/picture_layer.cc
 FILE: ../../../flutter/flow/layers/picture_layer.h
 FILE: ../../../flutter/flow/layers/platform_view_layer.cc

flow/BUILD.gn

@@ -98,6 +98,7 @@ executable("flow_unittests") {
     "flow_test_utils.cc",
     "flow_test_utils.h",
     "layers/performance_overlay_layer_unittests.cc",
+    "layers/physical_shape_layer_unittests.cc",
     "matrix_decomposition_unittests.cc",
     "raster_cache_unittests.cc",
   ]

flow/layers/container_layer.cc

@@ -27,8 +27,7 @@ void ContainerLayer::PrerollChildren(PrerollContext* context,
                                      const SkMatrix& child_matrix,
                                      SkRect* child_paint_bounds) {
   for (auto& layer : layers_) {
-    PrerollContext child_context = *context;
-    layer->Preroll(&child_context, child_matrix);
+    layer->Preroll(context, child_matrix);
 
     if (layer->needs_system_composite()) {
       set_needs_system_composite(true);

flow/layers/physical_shape_layer.cc

@@ -47,6 +47,7 @@ void PhysicalShapeLayer::Preroll(PrerollContext* context,
   total_elevation_ = context->total_elevation;
   SkRect child_paint_bounds;
   PrerollChildren(context, matrix, &child_paint_bounds);
+  context->total_elevation -= elevation_;
 
   if (elevation_ == 0) {
     set_paint_bounds(path_.getBounds());

flow/layers/physical_shape_layer.h

@@ -52,6 +52,8 @@ class PhysicalShapeLayer : public ContainerLayer {
   bool isRect_;
   SkRRect frameRRect_;
   Clip clip_behavior_;
+
+  friend class PhysicalShapeLayer_TotalElevation_Test;
 };
 
 }  // namespace flutter

flow/layers/physical_shape_layer_unittests.cc

+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/flow/layers/physical_shape_layer.h"
+
+#include "gtest/gtest.h"
+
+namespace flutter {
+
+TEST(PhysicalShapeLayer, TotalElevation) {
+  std::shared_ptr<PhysicalShapeLayer> layers[4];
+
+  for (int i = 0; i < 4; i += 1) {
+    layers[i] = std::make_shared<PhysicalShapeLayer>(Clip::none);
+    layers[i]->set_elevation((float)(i + 1));
+  }
+
+  layers[0]->Add(layers[1]);
+  layers[0]->Add(layers[2]);
+  layers[2]->Add(layers[3]);
+
+  const Stopwatch unused_stopwatch;
+  TextureRegistry unused_texture_registry;
+  PrerollContext preroll_context{
+      nullptr,                  // raster_cache (don't consult the cache)
+      nullptr,                  // gr_context  (used for the raster cache)
+      nullptr,                  // external view embedder
+      nullptr,                  // SkColorSpace* dst_color_space
+      kGiantRect,               // SkRect cull_rect
+      unused_stopwatch,         // frame time (dont care)
+      unused_stopwatch,         // engine time (dont care)
+      unused_texture_registry,  // texture registry (not supported)
+      false,                    // checkerboard_offscreen_layers
+      0.0f,                     // total elevation
+  };
+
+  SkMatrix identity;
+  identity.setIdentity();
+
+  layers[0]->Preroll(&preroll_context, identity);
+
+  // It should look like this:
+  // layers[0] +1.0f
+  // |       \
+  // |        \
+  // |         \
+  // |       layers[2] +3.0f
+  // |          |
+  // |       layers[3] +4.0f
+  // |
+  // |
+  // layers[1] + 2.0f
+  EXPECT_EQ(layers[0]->total_elevation_, 1.0f);
+  EXPECT_EQ(layers[1]->total_elevation_, 3.0f);
+  EXPECT_EQ(layers[2]->total_elevation_, 4.0f);
+  EXPECT_EQ(layers[3]->total_elevation_, 8.0f);
+}
+
+}  // namespace flutter