Improve dashed line drawing

third_party/WebKit/Source/platform/graphics/StrokeData.h

 // Copyright (C) 2013 Google Inc. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 69 matching lines @@
   // Setup any DashPathEffect on the paint. If a non-zero length is provided,
   // and no line dash has been set, the number of dashes/dots on a dashed/dotted
   // line will be adjusted to start and end that length with a dash/dot.
   void setupPaintDashPathEffect(PaintFlags*, int) const;
 
   // Determine whether a stroked line should be drawn using dashes. In practice,
   // we draw dashes when a dashed stroke is specified or when a dotted stroke
   // is specified but the line width is too small to draw circles.
   static bool strokeIsDashed(float width, StrokeStyle);
 
+  // The length of the dash relative to the line thickness for dashed stroking.
+  // A different dash length may be used when dashes are adjusted to better
+  // fit a given length path. Thin lines need longer dashes to avoid
+  // looking like dots when drawn.
+  static float dashLengthRatio(float thickness) {
+    return thickness >= 3 ? 2.0 : 3.0;
+  }
+
+  // The length of the gap between dashes relative to the line thickness for
+  // dashed stroking. A different gap may be used when dashes are adjusted to
+  // better fit a given length path. Thin lines need longer gaps to avoid
+  // looking like a continuous line when drawn.
+  static float dashGapRatio(float thickness) {
+    return thickness >= 3 ? 1.0 : 2.0;
+  }
+
+  // Return a dash gap size that places dashes at each end of a stroke that is
+  // strokeLength long, given preferred dash and gap sizes. The gap returned is
+  // the one that minimizes deviation from the preferred gap length.
+  static float selectBestDashGap(float strokeLength,
+                                 float dashLength,
+                                 float gapLength);
+
  private:
   StrokeStyle m_style;
   float m_thickness;
   PaintFlags::Cap m_lineCap;
   PaintFlags::Join m_lineJoin;
   float m_miterLimit;
   sk_sp<SkPathEffect> m_dash;
 };
 
 }  // namespace blink
 
 #endif  // StrokeData_h