Add alternative ambient shadow method to Android shadow sample

samplecode/SampleAndroidShadows.cpp

Index: samplecode/SampleAndroidShadows.cpp
diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
index 9ab69a670c8f98a8d977c9eadd98fdbadaddbb07..183eae037239cb6e74ea0594ce40c850f50bcf0e 100755
--- a/samplecode/SampleAndroidShadows.cpp
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -9,12 +9,15 @@
 #include "SkBlurMask.h"
 #include "SkBlurMaskFilter.h"
 #include "SkCanvas.h"
+#include "SkGaussianEdgeShader.h"
 #include "SkPath.h"
 #include "SkPoint3.h"
 #include "SkUtils.h"
 #include "SkView.h"
 #include "sk_tool_utils.h"
 
+////////////////////////////////////////////////////////////////////////////
+
 class ShadowsView : public SampleView {
     SkPath    fRectPath;
     SkPath    fRRPath;
@@ -120,10 +123,80 @@ protected:
         canvas->drawPath(path, paint);
 
         // draw occlusion rect
+#if DRAW_OCCL_RECT
         SkPaint stroke;
         stroke.setStyle(SkPaint::kStroke_Style);
         stroke.setColor(SK_ColorBLUE);
         canvas->drawRect(occlRect, stroke);
+#endif
+    }
+
+    void drawAmbientShadowAlt(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
+                              SkScalar ambientAlpha) {
+
+        if (ambientAlpha <= 0) {
+            return;
+        }
+
+        const SkScalar kHeightFactor = 1.f / 128.f;
+        const SkScalar kGeomFactor = 64;
+
+        SkScalar umbraAlpha = 1 / (1 + SkMaxScalar(zValue*kHeightFactor, 0));
+        SkScalar radius = zValue*kHeightFactor*kGeomFactor;
+
+        // fast path
+        SkRect pathRect;
+        SkRRect pathRRect;
+        if ((path.isOval(&pathRect) && pathRect.width() == pathRect.height()) ||
+            (path.isRRect(&pathRRect) && pathRRect.allCornersCircular()) ||
+            path.isRect(&pathRect)) {
+
+            // For all of these, we outset the rect by half the radius to get our stroke shape.
+            if (path.isOval(nullptr)) {
+                pathRect.outset(0.5f*radius, 0.5f*radius);
+                pathRRect = SkRRect::MakeOval(pathRect);
+            } else if (path.isRect(nullptr)) {
+                pathRect.outset(0.5f*radius, 0.5f*radius);
+                pathRRect = SkRRect::MakeRectXY(pathRect, 0.5f*radius, 0.5f*radius);
+            } else {
+                pathRRect.outset(0.5f*radius, 0.5f*radius);
+            }
+
+            SkPaint paint;
+            paint.setAntiAlias(true);
+            paint.setColor(SkColorSetARGB((unsigned char)(ambientAlpha*umbraAlpha*255.999f), 
+                                          0, 0, 0));
+            paint.setStrokeWidth(radius);
+            paint.setStyle(SkPaint::kStroke_Style);
+
+            sk_sp<SkShader> gaussShader = SkGaussianEdgeShader::Make();

[robertphillips, 2016/08/16 17:56:07]

std::move ?

[jvanverth1, 2016/08/16 19:14:11]

Done.

+            paint.setShader(gaussShader);
+            canvas->drawRRect(pathRRect, paint);
+        } else {
+            // occlude blur
+            SkRect occlRect;
+            GetOcclRect(path, &occlRect);
+            sk_sp<SkMaskFilter> f = SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
+                                                           SkBlurMask::ConvertRadiusToSigma(radius),
+                                                           occlRect,
+                                                           SkBlurMaskFilter::kNone_BlurFlag);
+
+            SkPaint paint;
+            paint.setAntiAlias(true);
+            paint.setMaskFilter(std::move(f));
+            paint.setColor(SkColorSetARGB((unsigned char)(ambientAlpha*umbraAlpha*255.999f), 
+                                          0, 0, 0));
+            canvas->drawPath(path, paint);
+
+            // draw occlusion rect
+#if DRAW_OCCL_RECT
+            SkPaint stroke;
+            stroke.setStyle(SkPaint::kStroke_Style);
+            stroke.setColor(SK_ColorBLUE);
+            canvas->drawRect(occlRect, stroke);
+#endif
+        }
+
     }
 
     void drawSpotShadow(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
@@ -178,10 +251,12 @@ protected:
         canvas->drawPath(path, paint);
 
         // draw occlusion rect
+#if DRAW_OCCL_RECT
         SkPaint stroke;
         stroke.setStyle(SkPaint::kStroke_Style);
         stroke.setColor(SK_ColorRED);
-        canvas->drawRect(occlRect, stroke);
+        canvas->drawRect(occlRect, stroke)
+#endif
     }
 
     void drawShadowedPath(SkCanvas* canvas, const SkPath& path, SkScalar zValue, 
@@ -191,7 +266,7 @@ protected:
         const SkScalar kSpotAlpha = 0.25f;
 
         if (fShowAmbient) {

[robertphillips, 2016/08/16 17:56:07]

Do we want to toggle between the two options ?

[jvanverth1, 2016/08/16 19:14:11]

Done.

-            this->drawAmbientShadow(canvas, path, zValue, kAmbientAlpha);
+            this->drawAmbientShadowAlt(canvas, path, zValue, kAmbientAlpha);
         }
         if (fShowSpot) {
             this->drawSpotShadow(canvas, path, zValue, fLightPos, kLightWidth, kSpotAlpha);
@@ -218,6 +293,10 @@ protected:
         paint.setColor(SK_ColorBLUE);
         canvas->translate(-250, 110);
         this->drawShadowedPath(canvas, fCirclePath, 5, paint);
+
+        paint.setColor(SK_ColorGREEN);
+        canvas->translate(250, 0);
+        this->drawShadowedPath(canvas, fRRPath, 5, paint);
     }
 
 protected: