[Text Decorations] Cache computed paths

The paths for wavy, dashed and dotted paths are quite expensive
to compute and are used in both bounds and painting. Cache them,
recomputing when needed and resetting when any line data changes.

No change in net behavior.

Bug: 896295
Change-Id: If0e58f49e6ecc9246b95d4b883eec1ac7d006ce6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2342641
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796244}

third_party/blink/renderer/core/paint/applied_decoration_painter.cc

@@ -35,7 +35,7 @@ void AppliedDecorationPainter::Paint() {
 
 void AppliedDecorationPainter::StrokeWavyTextDecoration() {
   context_.SetShouldAntialias(true);
-  context_.StrokePath(decoration_info_.PrepareWavyStrokePath(line_));
+  context_.StrokePath(decoration_info_.PrepareWavyStrokePath(line_).value());
 }
 
 }  // namespace blink

third_party/blink/renderer/core/paint/text_decoration_info.cc

@@ -194,6 +194,7 @@ void TextDecorationInfo::SetPerLineData(TextDecoration line,
   line_data_[index].line_offset = line_offset;
   line_data_[index].double_offset = double_offset;
   line_data_[index].wavy_offset_factor = wavy_offset_factor;
+  line_data_[index].stroke_path.reset();
 }
 
 ETextDecorationStyle TextDecorationInfo::DecorationStyle() const {
@@ -272,30 +273,35 @@ FloatRect TextDecorationInfo::BoundsForLine(TextDecoration line) const {
 
 FloatRect TextDecorationInfo::BoundsForDottedOrDashed(
     TextDecoration line) const {
-  // These coordinate transforms need to match what's happening in
-  // GraphicsContext's drawLineForText and drawLine.
-  FloatPoint start_point = StartPoint(line);
-  int y = floorf(start_point.Y() +
-                 std::max<float>(ResolvedThickness() / 2.0f, 0.5f));
-  FloatPoint rounded_start_point(start_point.X(), y);
-  FloatPoint rounded_end_point(rounded_start_point + FloatPoint(width_, 0));
-  GraphicsContext::AdjustLineToPixelBoundaries(
-      rounded_start_point, rounded_end_point, roundf(ResolvedThickness()));
-
-  Path stroke_path;
-  stroke_path.MoveTo(rounded_start_point);
-  stroke_path.AddLineTo(rounded_end_point);
+  int line_data_index = TextDecorationToLineDataIndex(line);
+  if (!line_data_[line_data_index].stroke_path) {
+    // These coordinate transforms need to match what's happening in
+    // GraphicsContext's drawLineForText and drawLine.
+    FloatPoint start_point = StartPoint(line);
+    int y = floorf(start_point.Y() +
+                   std::max<float>(ResolvedThickness() / 2.0f, 0.5f));
+    FloatPoint rounded_start_point(start_point.X(), y);
+    FloatPoint rounded_end_point(rounded_start_point + FloatPoint(width_, 0));
+    GraphicsContext::AdjustLineToPixelBoundaries(
+        rounded_start_point, rounded_end_point, roundf(ResolvedThickness()));
+
+    Path& stroke_path =
+        line_data_[TextDecorationToLineDataIndex(line)].stroke_path.emplace();
+    stroke_path.MoveTo(rounded_start_point);
+    stroke_path.AddLineTo(rounded_end_point);
+  }
 
   StrokeData stroke_data;
   stroke_data.SetThickness(ResolvedThickness());
   stroke_data.SetStyle(TextDecorationStyleToStrokeStyle(DecorationStyle()));
-  return stroke_path.StrokeBoundingRect(stroke_data);
+  return line_data_[line_data_index].stroke_path.value().StrokeBoundingRect(
+      stroke_data);
 }
 
 FloatRect TextDecorationInfo::BoundsForWavy(TextDecoration line) const {
   StrokeData stroke_data;
   stroke_data.SetThickness(ResolvedThickness());
-  return PrepareWavyStrokePath(line).StrokeBoundingRect(stroke_data);
+  return PrepareWavyStrokePath(line)->StrokeBoundingRect(stroke_data);
 }
 
 /*
@@ -325,7 +331,12 @@ FloatRect TextDecorationInfo::BoundsForWavy(TextDecoration line) const {
  *             |-----------|
  *                 step
  */
-Path TextDecorationInfo::PrepareWavyStrokePath(TextDecoration line) const {
+base::Optional<Path> TextDecorationInfo::PrepareWavyStrokePath(
+    TextDecoration line) const {
+  int line_data_index = TextDecorationToLineDataIndex(line);
+  if (line_data_[line_data_index].stroke_path)
+    return line_data_[line_data_index].stroke_path;
+
   FloatPoint start_point = StartPoint(line);
   float wave_offset =
       DoubleOffset(line) *
@@ -336,7 +347,7 @@ Path TextDecorationInfo::PrepareWavyStrokePath(TextDecoration line) const {
 
   GraphicsContext::AdjustLineToPixelBoundaries(p1, p2, ResolvedThickness());
 
-  Path path;
+  Path& path = line_data_[line_data_index].stroke_path.emplace();
   path.MoveTo(p1);
 
   // Distance between decoration's axis and Bezier curve's control points.
@@ -349,9 +360,10 @@ Path TextDecorationInfo::PrepareWavyStrokePath(TextDecoration line) const {
   // as strockThickness increases to make the curve looks better.
   float control_point_distance = 3 * std::max<float>(2, ResolvedThickness());
 
-  // Increment used to form the diamond shape between start point (p1), control
-  // points and end point (p2) along the axis of the decoration. Makes the
-  // curve wider as strockThickness increases to make the curve looks better.
+  // Increment used to form the diamond shape between start point (p1),
+  // control points and end point (p2) along the axis of the decoration. Makes
+  // the curve wider as strockThickness increases to make the curve looks
+  // better.
   float step = 2 * std::max<float>(2, ResolvedThickness());
 
   bool is_vertical_line = (p1.X() == p2.X());
@@ -409,7 +421,7 @@ Path TextDecorationInfo::PrepareWavyStrokePath(TextDecoration line) const {
                             FloatPoint(x, y_axis));
     }
   }
-  return path;
+  return line_data_[line_data_index].stroke_path;
 }
 
 }  // namespace blink

third_party/blink/renderer/core/paint/text_decoration_info.h

@@ -93,7 +93,7 @@ class CORE_EXPORT TextDecorationInfo {
 
   // Return a path for a wavy line at the given position, for the
   // current decoration.
-  Path PrepareWavyStrokePath(TextDecoration line) const;
+  base::Optional<Path> PrepareWavyStrokePath(TextDecoration line) const;
 
  private:
   float ComputeUnderlineThickness(
@@ -124,6 +124,7 @@ class CORE_EXPORT TextDecorationInfo {
     float line_offset;
     float double_offset;
     int wavy_offset_factor;
+    mutable base::Optional<Path> stroke_path;
   };
   PerLineData line_data_[3];
 };