Bug 1839474 - Add support for directly stroking circles to DrawTarget. r=lsalzman

D2D has a more efficient path when asked to stroke circles
vs. circular paths. This will let us use that.

Differential Revision: https://phabricator.services.mozilla.com/D181545

gfx/2d/2D.h

@@ -1544,6 +1544,18 @@ class DrawTarget : public external::AtomicRefCounted<DrawTarget> {
                           const StrokeOptions& aStrokeOptions = StrokeOptions(),
                           const DrawOptions& aOptions = DrawOptions()) = 0;
 
+  /**
+   * Stroke a circle on the DrawTarget with a certain source pattern.
+   *
+   * @param aCircle the parameters of the circle
+   * @param aPattern Pattern that forms the source of this stroking operation
+   * @param aOptions Options that are applied to this operation
+   */
+  virtual void StrokeCircle(
+      const Point& aOrigin, float radius, const Pattern& aPattern,
+      const StrokeOptions& aStrokeOptions = StrokeOptions(),
+      const DrawOptions& aOptions = DrawOptions());
+
   /**
    * Stroke a path on the draw target with a certain source pattern.
    *

gfx/2d/DrawTarget.cpp

@@ -179,6 +179,14 @@ void DrawTarget::FillRoundedRect(const RoundedRect& aRect,
   Fill(path, aPattern, aOptions);
 }
 
+void DrawTarget::StrokeCircle(const Point& aOrigin, float radius,
+                              const Pattern& aPattern,
+                              const StrokeOptions& aStrokeOptions,
+                              const DrawOptions& aOptions) {
+  RefPtr<Path> path = MakePathForCircle(*this, aOrigin, radius);
+  Stroke(path, aPattern, aStrokeOptions, aOptions);
+}
+
 void DrawTarget::StrokeGlyphs(ScaledFont* aFont, const GlyphBuffer& aBuffer,
                               const Pattern& aPattern,
                               const StrokeOptions& aStrokeOptions,

gfx/2d/PathHelpers.h

@@ -258,6 +258,15 @@ inline already_AddRefed<Path> MakePathForEllipse(const DrawTarget& aDrawTarget,
   return builder->Finish();
 }
 
+inline already_AddRefed<Path> MakePathForCircle(const DrawTarget& aDrawTarget,
+                                                const Point& aCenter,
+                                                float aRadius) {
+  RefPtr<PathBuilder> builder = aDrawTarget.CreatePathBuilder();
+  builder->Arc(aCenter, aRadius, 0.0f, Float(2.0 * M_PI));
+  builder->Close();
+  return builder->Finish();
+}
+
 /**
  * If aDrawTarget's transform only contains a translation, and if this line is
  * a horizontal or vertical line, this function will snap the line's vertices