Add a display list op to clear to transformation stack.

This allows for the implementation of the
DisplayListCanvasRecoder::didSetM44. Instead of another operation that
clears the transformation stack along with setting a new transformation
on it. A single no-payload operation that clears the stack is added.
Existing ops to push to the stack are then reused.

Author: chinmaygarde

DEPS

@@ -110,7 +110,7 @@ deps = {
   'src': 'https://github.com/flutter/buildroot.git' + '@' + '8cbf38af7d48cc298ae86e614533b4b2d0dc6758',
 
   'src/flutter/impeller':
-  Var('github_git') + '/flutter/impeller' + '@' + 'c1572a3335c4a533dacc28b86cbebdf08b5a57ed',
+  Var('github_git') + '/flutter/impeller' + '@' + 'b662deba147396d68e549e41d5d2d6b1cb0b0119',
 
    # Fuchsia compatibility
    #

display_list/display_list.h

@@ -103,6 +103,7 @@ namespace flutter {
   V(Skew)                           \
   V(Transform2DAffine)              \
   V(TransformFullPerspective)       \
+  V(TransformReset)                 \
                                     \
   V(ClipIntersectRect)              \
   V(ClipIntersectRRect)             \

display_list/display_list_builder.cc

@@ -427,8 +427,10 @@ void DisplayListBuilder::transformFullPerspective(
                                      mwx, mwy, mwz, mwt);
   }
 }
-
 // clang-format on
+void DisplayListBuilder::transformReset() {
+  Push<TransformResetOp>(0, 0);
+}
 
 void DisplayListBuilder::clipRect(const SkRect& rect,
                                   SkClipOp clip_op,

display_list/display_list_builder.h

@@ -176,8 +176,8 @@ class DisplayListBuilder final : public virtual Dispatcher,
       SkScalar myx, SkScalar myy, SkScalar myz, SkScalar myt,
       SkScalar mzx, SkScalar mzy, SkScalar mzz, SkScalar mzt,
       SkScalar mwx, SkScalar mwy, SkScalar mwz, SkScalar mwt) override;
-
   // clang-format on
+  void transformReset() override;
 
   void clipRect(const SkRect& rect, SkClipOp clip_op, bool is_aa) override;
   void clipRRect(const SkRRect& rrect, SkClipOp clip_op, bool is_aa) override;

display_list/display_list_canvas_dispatcher.cc

@@ -100,6 +100,9 @@ void DisplayListCanvasDispatcher::transformFullPerspective(
                         mwx, mwy, mwz, mwt));
 }
 // clang-format on
+void DisplayListCanvasDispatcher::transformReset() {
+  canvas_->resetMatrix();
+}
 
 void DisplayListCanvasDispatcher::clipRect(const SkRect& rect,
                                            SkClipOp clip_op,

display_list/display_list_canvas_dispatcher.h

@@ -46,6 +46,7 @@ class DisplayListCanvasDispatcher : public virtual Dispatcher,
       SkScalar mzx, SkScalar mzy, SkScalar mzz, SkScalar mzt,
       SkScalar mwx, SkScalar mwy, SkScalar mwz, SkScalar mwt) override;
   // clang-format on
+  void transformReset() override;
 
   void clipRect(const SkRect& rect, SkClipOp clip_op, bool is_aa) override;
   void clipRRect(const SkRRect& rrect, SkClipOp clip_op, bool is_aa) override;

display_list/display_list_canvas_recorder.cc

@@ -28,6 +28,10 @@ void DisplayListCanvasRecorder::didConcat44(const SkM44& m44) {
       m44.rc(3, 0), m44.rc(3, 1), m44.rc(3, 2), m44.rc(3, 3));
 }
 // clang-format on
+void DisplayListCanvasRecorder::didSetM44(const SkM44& matrix) {
+  builder_->transformReset();
+  didConcat44(matrix);
+}
 void DisplayListCanvasRecorder::didTranslate(SkScalar tx, SkScalar ty) {
   builder_->translate(tx, ty);
 }
@@ -230,11 +234,6 @@ void DisplayListCanvasRecorder::onDrawShadowRec(const SkPath& path,
                   << __FUNCTION__;
 }
 
-void DisplayListCanvasRecorder::didSetM44(const SkM44&) {
-  FML_DLOG(ERROR) << "Unimplemented DisplayListCanvasRecorder::"
-                  << __FUNCTION__;
-}
-
 void DisplayListCanvasRecorder::onDrawBehind(const SkPaint&) {
   FML_DLOG(ERROR) << "Unimplemented DisplayListCanvasRecorder::"
                   << __FUNCTION__;

display_list/display_list_dispatcher.h

@@ -168,9 +168,11 @@ class Dispatcher {
       SkScalar myx, SkScalar myy, SkScalar myz, SkScalar myt,
       SkScalar mzx, SkScalar mzy, SkScalar mzz, SkScalar mzt,
       SkScalar mwx, SkScalar mwy, SkScalar mwz, SkScalar mwt) = 0;
-
   // clang-format on
 
+  // Clears the transformation stack.
+  virtual void transformReset() = 0;
+
   virtual void clipRect(const SkRect& rect, SkClipOp clip_op, bool is_aa) = 0;
   virtual void clipRRect(const SkRRect& rrect,
                          SkClipOp clip_op,

display_list/display_list_ops.h

@@ -382,6 +382,15 @@ struct TransformFullPerspectiveOp final : DLOp {
   }
 };
 
+// 4 byte header with no payload.
+struct TransformResetOp final : DLOp {
+  static const auto kType = DisplayListOpType::kTransformReset;
+
+  TransformResetOp() = default;
+
+  void dispatch(Dispatcher& dispatcher) const { dispatcher.transformReset(); }
+};
+
 // 4 byte header + 4 byte common payload packs into minimum 8 bytes
 // SkRect is 16 more bytes, which packs efficiently into 24 bytes total
 // SkRRect is 52 more bytes, which rounds up to 56 bytes (4 bytes unused)

display_list/display_list_unittests.cc

@@ -1370,6 +1370,18 @@ TEST(DisplayList, DisplayListFullPerspectiveTransformHandling) {
   }
 }
 
+TEST(DisplayList, DisplayListTransformResetHandling) {
+  DisplayListBuilder builder;
+  builder.scale(20.0, 20.0);
+  builder.transformReset();
+  auto list = builder.Build();
+  ASSERT_NE(list, nullptr);
+  sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(10, 10);
+  SkCanvas* canvas = surface->getCanvas();
+  list->RenderTo(canvas);
+  ASSERT_TRUE(canvas->getTotalMatrix().isIdentity());
+}
+
 TEST(DisplayList, SingleOpsMightSupportGroupOpacityWithOrWithoutBlendMode) {
   auto run_tests = [](std::string name,
                       void build(DisplayListBuilder & builder),