add non-rendering operation culling to DisplayListBuilder (#41463)

This optimization avoids recording unnecessary render operations that will not affect the output and also eliminates the need for "draw detection" mechanisms like `DlOpSpy` and `CanvasSpy` by remembering if any non-transparent operations were included. The `DlOpSpy` unit tests were updated to check if the results from that object match the new `DisplayList::affects_transparent_surface()` method.

Fixes flutter/flutter#125338

In addition, this change will unblock some other Issues:

- flutter/flutter#125318
- flutter/flutter#125403

Author: flar

display_list/benchmarking/dl_complexity_unittests.cc

@@ -423,7 +423,7 @@ TEST(DisplayListComplexity, DrawAtlas) {
   std::vector<SkRSXform> xforms;
   for (int i = 0; i < 10; i++) {
     rects.push_back(SkRect::MakeXYWH(0, 0, 10, 10));
-    xforms.push_back(SkRSXform::Make(0, 0, 0, 0));
+    xforms.push_back(SkRSXform::Make(1, 0, 0, 0));
   }
 
   DisplayListBuilder builder;

display_list/display_list.cc

@@ -22,7 +22,8 @@ DisplayList::DisplayList()
       unique_id_(0),
       bounds_({0, 0, 0, 0}),
       can_apply_group_opacity_(true),
-      is_ui_thread_safe_(true) {}
+      is_ui_thread_safe_(true),
+      affects_transparent_surface_(false) {}
 
 DisplayList::DisplayList(DisplayListStorage&& storage,
                          size_t byte_count,
@@ -32,6 +33,7 @@ DisplayList::DisplayList(DisplayListStorage&& storage,
                          const SkRect& bounds,
                          bool can_apply_group_opacity,
                          bool is_ui_thread_safe,
+                         bool affects_transparent_surface,
                          sk_sp<const DlRTree> rtree)
     : storage_(std::move(storage)),
       byte_count_(byte_count),
@@ -42,6 +44,7 @@ DisplayList::DisplayList(DisplayListStorage&& storage,
       bounds_(bounds),
       can_apply_group_opacity_(can_apply_group_opacity),
       is_ui_thread_safe_(is_ui_thread_safe),
+      affects_transparent_surface_(affects_transparent_surface),
       rtree_(std::move(rtree)) {}
 
 DisplayList::~DisplayList() {

display_list/display_list.h

@@ -263,6 +263,9 @@ class DisplayList : public SkRefCnt {
   }
 
   bool can_apply_group_opacity() const { return can_apply_group_opacity_; }
+  bool affects_transparent_surface() const {
+    return affects_transparent_surface_;
+  }
   bool isUIThreadSafe() const { return is_ui_thread_safe_; }
 
  private:
@@ -274,6 +277,7 @@ class DisplayList : public SkRefCnt {
               const SkRect& bounds,
               bool can_apply_group_opacity,
               bool is_ui_thread_safe,
+              bool affects_transparent_surface,
               sk_sp<const DlRTree> rtree);
 
   static uint32_t next_unique_id();
@@ -292,6 +296,8 @@ class DisplayList : public SkRefCnt {
 
   const bool can_apply_group_opacity_;
   const bool is_ui_thread_safe_;
+  const bool affects_transparent_surface_;
+
   const sk_sp<const DlRTree> rtree_;
 
   void Dispatch(DlOpReceiver& ctx,

display_list/display_list_unittests.cc

@@ -22,6 +22,7 @@
 #include "flutter/testing/testing.h"
 
 #include "third_party/skia/include/core/SkPictureRecorder.h"
+#include "third_party/skia/include/core/SkRSXform.h"
 #include "third_party/skia/include/core/SkSurface.h"
 
 namespace flutter {
@@ -2636,5 +2637,164 @@ TEST_F(DisplayListTest, DrawSaveDrawCannotInheritOpacity) {
   ASSERT_FALSE(display_list->can_apply_group_opacity());
 }
 
+TEST_F(DisplayListTest, NopOperationsOmittedFromRecords) {
+  auto run_tests = [](const std::string& name,
+                      void init(DisplayListBuilder & builder, DlPaint & paint),
+                      uint32_t expected_op_count = 0u) {
+    auto run_one_test =
+        [init](const std::string& name,
+               void build(DisplayListBuilder & builder, DlPaint & paint),
+               uint32_t expected_op_count = 0u) {
+          DisplayListBuilder builder;
+          DlPaint paint;
+          init(builder, paint);
+          build(builder, paint);
+          auto list = builder.Build();
+          if (list->op_count() != expected_op_count) {
+            FML_LOG(ERROR) << *list;
+          }
+          ASSERT_EQ(list->op_count(), expected_op_count) << name;
+          ASSERT_TRUE(list->bounds().isEmpty()) << name;
+        };
+    run_one_test(
+        name + " DrawColor",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.DrawColor(paint.getColor(), paint.getBlendMode());
+        },
+        expected_op_count);
+    run_one_test(
+        name + " DrawPaint",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.DrawPaint(paint);
+        },
+        expected_op_count);
+    run_one_test(
+        name + " DrawRect",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.DrawRect({10, 10, 20, 20}, paint);
+        },
+        expected_op_count);
+    run_one_test(
+        name + " Other Draw Ops",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.DrawLine({10, 10}, {20, 20}, paint);
+          builder.DrawOval({10, 10, 20, 20}, paint);
+          builder.DrawCircle({50, 50}, 20, paint);
+          builder.DrawRRect(SkRRect::MakeRectXY({10, 10, 20, 20}, 5, 5), paint);
+          builder.DrawDRRect(SkRRect::MakeRectXY({5, 5, 100, 100}, 5, 5),
+                             SkRRect::MakeRectXY({10, 10, 20, 20}, 5, 5),
+                             paint);
+          builder.DrawPath(kTestPath1, paint);
+          builder.DrawArc({10, 10, 20, 20}, 45, 90, true, paint);
+          SkPoint pts[] = {{10, 10}, {20, 20}};
+          builder.DrawPoints(PointMode::kLines, 2, pts, paint);
+          builder.DrawVertices(TestVertices1, DlBlendMode::kSrcOver, paint);
+          builder.DrawImage(TestImage1, {10, 10}, DlImageSampling::kLinear,
+                            &paint);
+          builder.DrawImageRect(TestImage1, SkRect{0.0f, 0.0f, 10.0f, 10.0f},
+                                SkRect{10.0f, 10.0f, 25.0f, 25.0f},
+                                DlImageSampling::kLinear, &paint);
+          builder.DrawImageNine(TestImage1, {10, 10, 20, 20},
+                                {10, 10, 100, 100}, DlFilterMode::kLinear,
+                                &paint);
+          SkRSXform xforms[] = {{1, 0, 10, 10}, {0, 1, 10, 10}};
+          SkRect rects[] = {{10, 10, 20, 20}, {10, 20, 30, 20}};
+          builder.DrawAtlas(TestImage1, xforms, rects, nullptr, 2,
+                            DlBlendMode::kSrcOver, DlImageSampling::kLinear,
+                            nullptr, &paint);
+          builder.DrawTextBlob(TestBlob1, 10, 10, paint);
+
+          // Dst mode eliminates most rendering ops except for
+          // the following two, so we'll prune those manually...
+          if (paint.getBlendMode() != DlBlendMode::kDst) {
+            builder.DrawDisplayList(TestDisplayList1, paint.getOpacity());
+            builder.DrawShadow(kTestPath1, paint.getColor(), 1, true, 1);
+          }
+        },
+        expected_op_count);
+    run_one_test(
+        name + " SaveLayer",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.SaveLayer(nullptr, &paint, nullptr);
+          builder.DrawRect({10, 10, 20, 20}, DlPaint());
+          builder.Restore();
+        },
+        expected_op_count);
+    run_one_test(
+        name + " inside Save",
+        [](DisplayListBuilder& builder, DlPaint& paint) {
+          builder.Save();
+          builder.DrawRect({10, 10, 20, 20}, paint);
+          builder.Restore();
+        },
+        expected_op_count);
+  };
+  run_tests("transparent color",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              paint.setColor(DlColor::kTransparent());
+            });
+  run_tests("0 alpha",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              // The transparent test above already tested transparent
+              // black (all 0s), we set White color here so we can test
+              // the case of all 1s with a 0 alpha
+              paint.setColor(DlColor::kWhite());
+              paint.setAlpha(0);
+            });
+  run_tests("BlendMode::kDst",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              paint.setBlendMode(DlBlendMode::kDst);
+            });
+  run_tests("Empty rect clip",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              builder.ClipRect(SkRect::MakeEmpty(), ClipOp::kIntersect, false);
+            });
+  run_tests("Empty rrect clip",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              builder.ClipRRect(SkRRect::MakeEmpty(), ClipOp::kIntersect,
+                                false);
+            });
+  run_tests("Empty path clip",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              builder.ClipPath(SkPath(), ClipOp::kIntersect, false);
+            });
+  run_tests("Transparent SaveLayer",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              DlPaint save_paint;
+              save_paint.setColor(DlColor::kTransparent());
+              builder.SaveLayer(nullptr, &save_paint);
+            });
+  run_tests("0 alpha SaveLayer",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              DlPaint save_paint;
+              // The transparent test above already tested transparent
+              // black (all 0s), we set White color here so we can test
+              // the case of all 1s with a 0 alpha
+              save_paint.setColor(DlColor::kWhite());
+              save_paint.setAlpha(0);
+              builder.SaveLayer(nullptr, &save_paint);
+            });
+  run_tests("Dst blended SaveLayer",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              DlPaint save_paint;
+              save_paint.setBlendMode(DlBlendMode::kDst);
+              builder.SaveLayer(nullptr, &save_paint);
+            });
+  run_tests(
+      "Nop inside SaveLayer",
+      [](DisplayListBuilder& builder, DlPaint& paint) {
+        builder.SaveLayer(nullptr, nullptr);
+        paint.setBlendMode(DlBlendMode::kDst);
+      },
+      2u);
+  run_tests("DrawImage inside Culled SaveLayer",  //
+            [](DisplayListBuilder& builder, DlPaint& paint) {
+              DlPaint save_paint;
+              save_paint.setColor(DlColor::kTransparent());
+              builder.SaveLayer(nullptr, &save_paint);
+              builder.DrawImage(TestImage1, {10, 10}, DlImageSampling::kLinear);
+            });
+}
+
 }  // namespace testing
 }  // namespace flutter