Implement tilted concave ambient shadow

Bug: skia:7971
Change-Id: I6a92a5021f53ae10fb35ef355081653e96bc04b0
Reviewed-on: https://skia-review.googlesource.com/134844
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

2 files changed, 19 insertions, 3 deletions

diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
index ee833d7939..cdc9e75201 100644
--- a/samplecode/SampleAndroidShadows.cpp
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -315,6 +315,7 @@ protected:
                               fWideOvalPath.getBounds().height() / 2);
         translate = SkPoint::Make(100, 600);
         view.restore();
+        view.save();
         view.rotateY(fAnimAngle);
         view.getMatrix(&persp);
         persp.preTranslate(-pivot.fX, -pivot.fY);
@@ -325,6 +326,21 @@ protected:
                                       SkTMax(1.0f, 32 + fZDelta) + SkScalarSin(radians)*pivot.fX);
         this->drawShadowedPath(canvas, fWideOvalPath, zPlaneParams, paint, .1f,
                                lightPos, kLightWidth, .5f);
+
+        pivot = SkPoint::Make(fStarPath.getBounds().width() / 2,
+                              fStarPath.getBounds().height() / 2);
+        translate = SkPoint::Make(700, 250);
+        view.restore();
+        view.rotateY(fAnimAngle);
+        view.getMatrix(&persp);
+        persp.preTranslate(-pivot.fX, -pivot.fY);
+        persp.postTranslate(pivot.fX + translate.fX, pivot.fY + translate.fY);
+        canvas->setMatrix(persp);
+        zPlaneParams = SkPoint3::Make(-SkScalarSin(radians),
+                                      0,
+                                      SkTMax(1.0f, 8 + fZDelta) + SkScalarSin(radians)*pivot.fX);
+        this->drawShadowedPath(canvas, fStarPath, zPlaneParams, paint, .1f,
+                               lightPos, kLightWidth, .5f);
     }
 
     bool onAnimate(const SkAnimTimer& timer) override {
diff --git a/src/utils/SkShadowTessellator.cpp b/src/utils/SkShadowTessellator.cpp
index c50265fd42..79f8f22636 100755
--- a/src/utils/SkShadowTessellator.cpp
+++ b/src/utils/SkShadowTessellator.cpp
@@ -794,9 +794,9 @@ bool SkAmbientShadowTessellator::computeConcaveShadow() {
     SkTDArray<int> penumbraIndices;
     penumbraPolygon.setReserve(umbraPolygon.count());
     penumbraIndices.setReserve(umbraPolygon.count());
-    // TODO: handle tilt
-    SkScalar radius = this->offset(fTransformedHeightFunc(fPathPolygon[0]));
-    if (!SkOffsetSimplePolygon(&fPathPolygon[0], fPathPolygon.count(), -radius,
+
+    auto offsetFunc = [this](const SkPoint& p) { return -this->offset(fTransformedHeightFunc(p)); };
+    if (!SkOffsetSimplePolygon(&fPathPolygon[0], fPathPolygon.count(), offsetFunc,
                                &penumbraPolygon, &penumbraIndices)) {
         // TODO: figure out how to handle this case
         return false;