Add Android Shadow sample

samplecode/SampleAndroidShadows.cpp

Index: samplecode/SampleAndroidShadows.cpp
diff --git a/samplecode/SampleAndroidShadows.cpp b/samplecode/SampleAndroidShadows.cpp
new file mode 100755
index 0000000000000000000000000000000000000000..9ab69a670c8f98a8d977c9eadd98fdbadaddbb07
--- /dev/null
+++ b/samplecode/SampleAndroidShadows.cpp
@@ -0,0 +1,251 @@
+
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SampleCode.h"
+#include "SkBlurMask.h"
+#include "SkBlurMaskFilter.h"
+#include "SkCanvas.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;
+    SkPath    fCirclePath;
+    SkPoint3  fLightPos;
+
+    bool      fShowAmbient;
+    bool      fShowSpot;
+    bool      fShowObject;
+
+public:
+    ShadowsView() 
+        : fShowAmbient(true)
+        , fShowSpot(true)
+        , fShowObject(true) {}
+
+protected:
+    void onOnceBeforeDraw() override {
+        fCirclePath.addCircle(0, 0, 50);
+        fRectPath.addRect(SkRect::MakeXYWH(-100, -50, 200, 100));
+        fRRPath.addRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(-100, -50, 200, 100), 4, 4));
+        fLightPos = SkPoint3::Make(-220, -330, 150);
+    }
+
+    // overrides from SkEventSink
+    bool onQuery(SkEvent* evt) override {
+        if (SampleCode::TitleQ(*evt)) {
+            SampleCode::TitleR(evt, "AndroidShadows");
+            return true;
+        }
+
+        SkUnichar uni;
+        if (SampleCode::CharQ(*evt, &uni)) {
+            switch (uni) {
+                case 'B':
+                    fShowAmbient = !fShowAmbient;
+                    break;
+                case 'S':
+                    fShowSpot = !fShowSpot;
+                    break;
+                case 'O':
+                    fShowObject = !fShowObject;
+                    break;
+                case '>':
+                    fLightPos.fZ += 10;
+                    break;
+                case '<':
+                    fLightPos.fZ -= 10;
+                    break;
+                default:
+                    break;
+            }
+            this->inval(nullptr);
+        }
+        return this->INHERITED::onQuery(evt);
+    }
+
+    void drawBG(SkCanvas* canvas) {
+        canvas->drawColor(0xFFDDDDDD);
+    }
+
+    static void GetOcclRect(const SkPath& path, SkRect* occlRect) {
+        SkRect pathRect;
+        SkRRect pathRRect;
+        if (path.isOval(&pathRect)) {
+            *occlRect = sk_tool_utils::compute_central_occluder(SkRRect::MakeOval(pathRect));
+        } else if (path.isRRect(&pathRRect)) {
+            *occlRect = sk_tool_utils::compute_central_occluder(pathRRect);
+        } else if (path.isRect(occlRect)) {
+            // the inverse transform for the spot shadow occluder doesn't always get us
+            // back to exactly the same position, so deducting a little slop
+            occlRect->inset(1, 1);
+        } else {
+            *occlRect = SkRect::MakeEmpty();
+        }
+    }
+
+    void drawAmbientShadow(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;
+
+        // occlude blur
+        SkRect occlRect;
+        GetOcclRect(path, &occlRect);
+        sk_sp<SkMaskFilter> mf = SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
+                                                        SkBlurMask::ConvertRadiusToSigma(radius),
+                                                        occlRect,
+                                                        SkBlurMaskFilter::kNone_BlurFlag);
+
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        paint.setMaskFilter(std::move(mf));
+        paint.setColor(SkColorSetARGB((unsigned char)(ambientAlpha*umbraAlpha*255.999f), 0, 0, 0));
+        canvas->drawPath(path, paint);
+
+        // draw occlusion rect
+        SkPaint stroke;
+        stroke.setStyle(SkPaint::kStroke_Style);
+        stroke.setColor(SK_ColorBLUE);
+        canvas->drawRect(occlRect, stroke);
+    }
+
+    void drawSpotShadow(SkCanvas* canvas, const SkPath& path, SkScalar zValue,
+                        SkPoint3 lightPos, SkScalar lightWidth, SkScalar spotAlpha) {
+        if (spotAlpha <= 0) {
+            return;
+        }
+
+        SkScalar zRatio = zValue / (lightPos.fZ - zValue);
+        if (zRatio < 0.0f) {
+            zRatio = 0.0f;
+        } else if (zRatio > 0.95f) {
+            zRatio = 0.95f;
+        }
+        SkScalar radius = lightWidth*zRatio;
+
+        // compute the transformation params
+        SkPoint center = SkPoint::Make(path.getBounds().centerX(), path.getBounds().centerY());
+        canvas->getTotalMatrix().mapPoints(&center, 1);
+        SkPoint offset = SkPoint::Make(-zRatio*(lightPos.fX - center.fX), 
+                                       -zRatio*(lightPos.fY - center.fY));
+        SkScalar scale = lightPos.fZ / (lightPos.fZ - zValue);
+        if (scale < 1.0f) {
+            scale = 1.0f;
+        } else if (scale > 1024.f) {
+            scale = 1024.f;
+        }
+
+        SkAutoCanvasRestore acr(canvas, true);
+
+        SkRect occlRect;
+        GetOcclRect(path, &occlRect);
+        // apply inverse transform
+        occlRect.offset(-offset);
+        occlRect.fLeft /= scale;
+        occlRect.fRight /= scale;
+        occlRect.fTop /= scale;
+        occlRect.fBottom /= scale;
+        sk_sp<SkMaskFilter> mf = SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
+                                                        SkBlurMask::ConvertRadiusToSigma(radius),
+                                                        occlRect,
+                                                        SkBlurMaskFilter::kNone_BlurFlag);
+
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        paint.setMaskFilter(std::move(mf));
+        paint.setColor(SkColorSetARGB((unsigned char)(spotAlpha*255.999f), 0, 0, 0));
+
+        // apply transformation to shadow
+        canvas->translate(offset.fX, offset.fY);
+        canvas->scale(scale, scale);
+        canvas->drawPath(path, paint);
+
+        // draw occlusion rect
+        SkPaint stroke;
+        stroke.setStyle(SkPaint::kStroke_Style);
+        stroke.setColor(SK_ColorRED);
+        canvas->drawRect(occlRect, stroke);
+    }
+
+    void drawShadowedPath(SkCanvas* canvas, const SkPath& path, SkScalar zValue, 
+                          const SkPaint& paint) {
+        const SkScalar kLightWidth = 3;
+        const SkScalar kAmbientAlpha = 0.25f;
+        const SkScalar kSpotAlpha = 0.25f;
+
+        if (fShowAmbient) {
+            this->drawAmbientShadow(canvas, path, zValue, kAmbientAlpha);
+        }
+        if (fShowSpot) {
+            this->drawSpotShadow(canvas, path, zValue, fLightPos, kLightWidth, kSpotAlpha);
+        }
+        if (fShowObject) {
+            canvas->drawPath(path, paint);
+        }
+    }
+
+    void onDrawContent(SkCanvas* canvas) override {
+        this->drawBG(canvas);
+
+        SkPaint paint;
+        paint.setAntiAlias(true);
+
+        paint.setColor(SK_ColorWHITE);
+        canvas->translate(200, 90);
+        this->drawShadowedPath(canvas, fRectPath, 5, paint);
+
+        paint.setColor(SK_ColorRED);
+        canvas->translate(250, 0);
+        this->drawShadowedPath(canvas, fRRPath, 5, paint);
+
+        paint.setColor(SK_ColorBLUE);
+        canvas->translate(-250, 110);
+        this->drawShadowedPath(canvas, fCirclePath, 5, paint);
+    }
+
+protected:
+    SkView::Click* onFindClickHandler(SkScalar x, SkScalar y, unsigned modi) override {
+        return new SkView::Click(this);
+    }
+
+    bool onClick(Click *click) override {
+        SkScalar x = click->fCurr.fX;
+        SkScalar y = click->fCurr.fY;
+
+        SkScalar dx = x - click->fPrev.fX;
+        SkScalar dy = y - click->fPrev.fY;
+
+        if (dx != 0 || dy != 0) {
+            fLightPos.fX += dx;
+            fLightPos.fY += dy;
+            this->inval(nullptr);
+        }
+
+        return true;
+    }
+
+private:
+    typedef SkView INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static SkView* MyFactory() { return new ShadowsView; }
+static SkViewRegister reg(MyFactory);