Circular shadow fixes for Flutter.

* Fix spot shadow placement for SkSpotShadowMaskFilter.
* Make sure we don't try to render an oval as a plain RRect
  due to floating point error.
* Use fast path for uncached circles.
* Make sure ShadowMaskFilters can handle near-circles.

Change-Id: Ia9967a00a6e1c980a1c0a7ba8248f09fde61a3b7
Reviewed-on: https://skia-review.googlesource.com/13969
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

1 files changed, 22 insertions, 2 deletions

diff --git a/src/utils/SkShadowUtils.cpp b/src/utils/SkShadowUtils.cpp
index 2e560b454e..8206bd3f54 100644
--- a/src/utils/SkShadowUtils.cpp
+++ b/src/utils/SkShadowUtils.cpp
@@ -471,12 +471,12 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar oc
         if (ambientAlpha > 0) {
             newPaint.setMaskFilter(SkAmbientShadowMaskFilter::Make(occluderHeight, ambientAlpha,
                                                                    flags));
-            canvas->drawPath(path, newPaint);
+            canvas->drawOval(rect, newPaint);
         }
         if (spotAlpha > 0) {
             newPaint.setMaskFilter(SkSpotShadowMaskFilter::Make(occluderHeight, devLightPos,
                                                                 lightRadius, spotAlpha, flags));
-            canvas->drawPath(path, newPaint);
+            canvas->drawOval(rect, newPaint);
         }
         return;
     }
@@ -565,6 +565,26 @@ void SkShadowUtils::DrawUncachedShadow(SkCanvas* canvas, const SkPath& path,
                                        uint32_t flags) {
     SkAutoCanvasRestore acr(canvas, true);
     SkMatrix viewMatrix = canvas->getTotalMatrix();
+
+    // try circular fast path
+    SkRect rect;
+    if (viewMatrix.isSimilarity() &&
+        path.isOval(&rect) && rect.width() == rect.height()) {
+        SkPaint newPaint;
+        newPaint.setColor(color);
+        if (ambientAlpha > 0) {
+            newPaint.setMaskFilter(SkAmbientShadowMaskFilter::Make(heightFunc(0,0), ambientAlpha,
+                                                                   flags));
+            canvas->drawOval(rect, newPaint);
+        }
+        if (spotAlpha > 0) {
+            newPaint.setMaskFilter(SkSpotShadowMaskFilter::Make(heightFunc(0,0), lightPos,
+                                                                lightRadius, spotAlpha, flags));
+            canvas->drawOval(rect, newPaint);
+        }
+        return;
+    }
+
     canvas->resetMatrix();
 
     bool transparent = SkToBool(flags & SkShadowFlags::kTransparentOccluder_ShadowFlag);