optimize out unnecessary save restore pairs

display_list/display_list_builder.cc

@@ -4,6 +4,7 @@
 
 #include "flutter/display_list/display_list_builder.h"
 
+#include "flutter/display_list/display_list.h"
 #include "flutter/display_list/display_list_blend_mode.h"
 #include "flutter/display_list/display_list_ops.h"
 
@@ -413,19 +414,29 @@ void DisplayListBuilder::setAttributesFromPaint(
   }
 }
 
+void DisplayListBuilder::checkForDeferredSave() {
+  if (current_layer_->has_deferred_save_op_) {
+    Push<SaveOp>(0, 1);
+    current_layer_->has_deferred_save_op_ = false;
+  }
+}
+
 void DisplayListBuilder::save() {
-  Push<SaveOp>(0, 1);
   layer_stack_.emplace_back(current_layer_);
   current_layer_ = &layer_stack_.back();
+  current_layer_->has_deferred_save_op_ = true;
 }
+
 void DisplayListBuilder::restore() {
   if (layer_stack_.size() > 1) {
+    if (!current_layer_->has_deferred_save_op_) {
+      Push<RestoreOp>(0, 1);
+    }
     // Grab the current layer info before we push the restore
     // on the stack.
     LayerInfo layer_info = layer_stack_.back();
     layer_stack_.pop_back();
     current_layer_ = &layer_stack_.back();
-    Push<RestoreOp>(0, 1);
     if (layer_info.has_layer) {
       if (layer_info.is_group_opacity_compatible()) {
         // We are now going to go back and modify the matching saveLayer
@@ -504,26 +515,30 @@ void DisplayListBuilder::saveLayer(const SkRect* bounds,
 void DisplayListBuilder::translate(SkScalar tx, SkScalar ty) {
   if (SkScalarIsFinite(tx) && SkScalarIsFinite(ty) &&
       (tx != 0.0 || ty != 0.0)) {
+    checkForDeferredSave();
     Push<TranslateOp>(0, 1, tx, ty);
     current_layer_->matrix.preTranslate(tx, ty);
   }
 }
 void DisplayListBuilder::scale(SkScalar sx, SkScalar sy) {
   if (SkScalarIsFinite(sx) && SkScalarIsFinite(sy) &&
       (sx != 1.0 || sy != 1.0)) {
+    checkForDeferredSave();
     Push<ScaleOp>(0, 1, sx, sy);
     current_layer_->matrix.preScale(sx, sy);
   }
 }
 void DisplayListBuilder::rotate(SkScalar degrees) {
   if (SkScalarMod(degrees, 360.0) != 0.0) {
+    checkForDeferredSave();
     Push<RotateOp>(0, 1, degrees);
     current_layer_->matrix.preConcat(SkMatrix::RotateDeg(degrees));
   }
 }
 void DisplayListBuilder::skew(SkScalar sx, SkScalar sy) {
   if (SkScalarIsFinite(sx) && SkScalarIsFinite(sy) &&
       (sx != 0.0 || sy != 0.0)) {
+    checkForDeferredSave();
     Push<SkewOp>(0, 1, sx, sy);
     current_layer_->matrix.preConcat(SkMatrix::Skew(sx, sy));
   }
@@ -540,6 +555,7 @@ void DisplayListBuilder::transform2DAffine(
       SkScalarsAreFinite(mxt, myt) &&
       !(mxx == 1 && mxy == 0 && mxt == 0 &&
         myx == 0 && myy == 1 && myt == 0)) {
+    checkForDeferredSave();
     Push<Transform2DAffineOp>(0, 1,
                               mxx, mxy, mxt,
                               myx, myy, myt);
@@ -565,6 +581,7 @@ void DisplayListBuilder::transformFullPerspective(
              SkScalarsAreFinite(myx, myy) && SkScalarsAreFinite(myz, myt) &&
              SkScalarsAreFinite(mzx, mzy) && SkScalarsAreFinite(mzz, mzt) &&
              SkScalarsAreFinite(mwx, mwy) && SkScalarsAreFinite(mwz, mwt)) {
+    checkForDeferredSave();
     Push<TransformFullPerspectiveOp>(0, 1,
                                      mxx, mxy, mxz, mxt,
                                      myx, myy, myz, myt,
@@ -578,6 +595,7 @@ void DisplayListBuilder::transformFullPerspective(
 }
 // clang-format on
 void DisplayListBuilder::transformReset() {
+  checkForDeferredSave();
   Push<TransformResetOp>(0, 0);
   current_layer_->matrix.setIdentity();
 }
@@ -599,6 +617,10 @@ void DisplayListBuilder::transform(const SkM44* m44) {
 void DisplayListBuilder::clipRect(const SkRect& rect,
                                   SkClipOp clip_op,
                                   bool is_aa) {
+  if (!rect.isFinite()) {
+    return;
+  }
+  checkForDeferredSave();
   switch (clip_op) {
     case SkClipOp::kIntersect:
       Push<ClipIntersectRectOp>(0, 1, rect, is_aa);
@@ -615,6 +637,7 @@ void DisplayListBuilder::clipRRect(const SkRRect& rrect,
   if (rrect.isRect()) {
     clipRect(rrect.rect(), clip_op, is_aa);
   } else {
+    checkForDeferredSave();
     switch (clip_op) {
       case SkClipOp::kIntersect:
         Push<ClipIntersectRRectOp>(0, 1, rrect, is_aa);
@@ -646,6 +669,7 @@ void DisplayListBuilder::clipPath(const SkPath& path,
       return;
     }
   }
+  checkForDeferredSave();
   switch (clip_op) {
     case SkClipOp::kIntersect:
       Push<ClipIntersectPathOp>(0, 1, path, is_aa);

display_list/display_list_builder.h

@@ -343,6 +343,8 @@ class DisplayListBuilder final : public virtual Dispatcher,
   sk_sp<DisplayList> Build();
 
  private:
+  void checkForDeferredSave();
+
   SkAutoTMalloc<uint8_t> storage_;
   size_t used_ = 0;
   size_t allocated_ = 0;
@@ -397,6 +399,8 @@ class DisplayListBuilder final : public virtual Dispatcher,
     // This offset is only valid if |has_layer| is true.
     size_t save_layer_offset;
 
+    bool has_deferred_save_op_ = false;
+
     bool has_layer;
     bool cannot_inherit_opacity;
     bool has_compatible_op;