Add GM/slide to simulate Android-style reveal clip

gm/reveal.cpp

Index: gm/reveal.cpp
diff --git a/gm/reveal.cpp b/gm/reveal.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..de36c0e8d43898d6daac3f31ca61bd39f82af651
--- /dev/null
+++ b/gm/reveal.cpp
@@ -0,0 +1,332 @@
+/*
+ * 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 "gm.h"
+#include "SkAnimTimer.h"
+#include "SkBlurMaskFilter.h"
+#include "SkGaussianEdgeShader.h"
+#include "SkPath.h"
+#include "SkPathOps.h"
+#include "SkRRect.h"
+#include "SkStroke.h"
+
+constexpr int kNumCols = 2;
+constexpr int kNumRows = 5;
+constexpr int kCellSize = 128;
+constexpr SkScalar kPad = 8.0f;
+constexpr SkScalar kPeriod = 8.0f;
+constexpr int kClipOffset = 32;
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+typedef SkPath (*PFDrawMthd)(SkCanvas*, const SkRect&, bool);
+
+static SkPath draw_rrect(SkCanvas* canvas, const SkRect& r, bool stroked) {
+    SkRRect rr = SkRRect::MakeRectXY(r, 2*kPad, 2*kPad);
+
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    if (stroked) {
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setColor(SK_ColorRED);
+    } else {
+        // G channel is an F6.2 radius
+        paint.setColor(SkColorSetARGB(255, 255, (unsigned char)(4*kPad), 0));
+        paint.setShader(SkGaussianEdgeShader::Make());
+    }
+    canvas->drawRRect(rr, paint);
+
+    SkPath p;
+    p.addRoundRect(r, 2*kPad, 2*kPad);
+    return p;
+}
+
+static SkPath draw_stroked_rrect(SkCanvas* canvas, const SkRect& r, bool stroked) {
+    SkRect insetRect = r;
+    insetRect.inset(kPad, kPad);
+    SkRRect rr = SkRRect::MakeRectXY(insetRect, 2*kPad, 2*kPad);
+
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(kPad);
+
+    if (stroked) {
+        // In this case we want to draw a stroked representation of the stroked rrect
+        SkPath p, stroked;
+        p.addRRect(rr);
+        SkStroke stroke(paint);
+        stroke.strokePath(p, &stroked);
+
+        paint.setStrokeWidth(0);
+        paint.setColor(SK_ColorRED);
+        canvas->drawPath(stroked, paint);
+    } else {
+        // G channel is an F6.2 radius
+        paint.setColor(SkColorSetARGB(255, 255, (unsigned char)(4*kPad), 0));
+        paint.setShader(SkGaussianEdgeShader::Make());
+
+        canvas->drawRRect(rr, paint);
+    }
+
+    SkPath p;
+    insetRect.outset(kPad/2.0f, kPad/2.0f);
+    p.addRoundRect(insetRect, 2*kPad, 2*kPad);
+    return p;
+}
+
+static SkPath draw_oval(SkCanvas* canvas, const SkRect& r, bool stroked) {
+    SkRRect rr = SkRRect::MakeOval(r);
+
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    if (stroked) {
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setColor(SK_ColorRED);
+    } else {
+        // G channel is an F6.2 radius
+        paint.setColor(SkColorSetARGB(255, 255, (unsigned char)(4*kPad), 0));
+        paint.setShader(SkGaussianEdgeShader::Make());
+    }
+    canvas->drawRRect(rr, paint);
+
+    SkPath p;
+    p.addOval(r);
+    return p;
+}
+
+static SkPath draw_square(SkCanvas* canvas, const SkRect& r, bool stroked) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    if (stroked) {
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setColor(SK_ColorRED);
+    } else {
+        // G channel is an F6.2 radius
+        paint.setColor(SkColorSetARGB(255, 255, (unsigned char)(4*kPad), 0));
+        paint.setShader(SkGaussianEdgeShader::Make());
+    }
+    canvas->drawRect(r, paint);
+
+    SkPath p;
+    p.addRect(r);
+    return p;
+}
+
+static SkPath draw_pentagon(SkCanvas* canvas, const SkRect& r, bool stroked) {
+    SkPath p;
+
+    SkPoint points[5] = {
+        {  0.000000f, -1.000000f },
+        { -0.951056f, -0.309017f },
+        { -0.587785f,  0.809017f },
+        {  0.587785f,  0.809017f },
+        {  0.951057f, -0.309017f },
+    };
+
+    SkScalar height = r.height()/2.0f;
+    SkScalar width = r.width()/2.0f;
+
+    p.moveTo(r.centerX() + points[0].fX * width, r.centerY() + points[0].fY * height);
+    p.lineTo(r.centerX() + points[1].fX * width, r.centerY() + points[1].fY * height);
+    p.lineTo(r.centerX() + points[2].fX * width, r.centerY() + points[2].fY * height);
+    p.lineTo(r.centerX() + points[3].fX * width, r.centerY() + points[3].fY * height);
+    p.lineTo(r.centerX() + points[4].fX * width, r.centerY() + points[4].fY * height);
+    p.close();
+
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    if (stroked) {
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setColor(SK_ColorRED);
+    } else {
+        // G channel is an F6.2 radius
+        paint.setColor(SkColorSetARGB(255, 255, (unsigned char)(4*kPad), 0));
+        // This currently goes through the GrAAConvexPathRenderer and produces a
+        // AAConvexPathBatch (i.e., it doesn't have a analytic distance)
+        // paint.setShader(SkGaussianEdgeShader::Make());
+    }
+    canvas->drawPath(p, paint);
+
+    return p;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+typedef void (*PFClipMthd)(SkCanvas* canvas, const SkPoint&, SkScalar);
+
+static void circle_clip(SkCanvas* canvas, const SkPoint& center, SkScalar rad) {
+    SkRect r = SkRect::MakeLTRB(center.fX - rad, center.fY - rad, center.fX + rad, center.fY + rad);
+    SkRRect rr = SkRRect::MakeOval(r);
+
+    canvas->clipRRect(rr);
+}
+
+static void square_clip(SkCanvas* canvas, const SkPoint& center, SkScalar size) {
+    SkScalar newSize = SK_ScalarRoot2Over2 * size;
+    SkRect r = SkRect::MakeLTRB(center.fX - newSize, center.fY - newSize,
+                                center.fX + newSize, center.fY + newSize);
+
+    canvas->clipRect(r);
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+// These are stand alone methods (rather than just, say, returning the SkPath for the clip 
+// object) so that we can catch the clip-contains-victim case.
+typedef SkPath (*PFGeometricClipMthd)(const SkPoint&, SkScalar, const SkPath&);
+
+static SkPath circle_geometric_clip(const SkPoint& center, SkScalar rad, const SkPath& victim) {
+    const SkRect bound = victim.getBounds();
+    SkPoint pts[4];
+    bound.toQuad(pts);
+
+    bool clipContainsVictim = true;
+    for (int i = 0; i < 4; ++i) {
+        SkScalar distSq = (pts[i].fX - center.fX) * (pts[i].fX - center.fX) +
+                          (pts[i].fY - center.fY) * (pts[i].fY - center.fY);
+        if (distSq >= rad*rad) {
+            clipContainsVictim = false;
+        }
+    }
+
+    if (clipContainsVictim) {
+        return victim;
+    }
+
+    // Add victim contains clip test?
+
+    SkPath clipPath;
+    clipPath.addCircle(center.fX, center.fY, rad);
+
+    SkPath result;
+    SkAssertResult(Op(clipPath, victim, kIntersect_SkPathOp, &result));
+
+    return result;
+}
+
+static SkPath square_geometric_clip(const SkPoint& center, SkScalar size, const SkPath& victim) {
+    SkScalar newSize = SK_ScalarRoot2Over2 * size;
+    SkRect r = SkRect::MakeLTRB(center.fX - newSize, center.fY - newSize,
+                                center.fX + newSize, center.fY + newSize);
+
+    const SkRect bound = victim.getBounds();
+
+    if (r.contains(bound)) {
+        return victim;
+    }
+
+    // Add victim contains clip test?
+
+    SkPath clipPath;
+    clipPath.addRect(r);
+
+    SkPath result;
+    SkAssertResult(Op(clipPath, victim, kIntersect_SkPathOp, &result));
+
+    return result;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+namespace skiagm {
+
+// This GM attempts to mimic Android's reveal animation
+class RevealGM : public GM {
+public:
+    RevealGM() : fFraction(0.5f), fDrawWithGaussianEdge(true) {
+        this->setBGColor(sk_tool_utils::color_to_565(0xFFCCCCCC));
+    }
+
+protected:
+
+    SkString onShortName() override {
+        return SkString("reveal");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(kNumCols * kCellSize, kNumRows * kCellSize);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        PFClipMthd clips[kNumCols] = { circle_clip, square_clip };
+        PFGeometricClipMthd geometricClips[kNumCols] = {
+            circle_geometric_clip, 
+            square_geometric_clip
+        };
+        PFDrawMthd draws[kNumRows] = {
+            draw_rrect,
+            draw_stroked_rrect,
+            draw_oval,
+            draw_square,
+            draw_pentagon
+        };
+
+        SkPaint strokePaint;
+        strokePaint.setColor(SK_ColorGREEN);
+        strokePaint.setStyle(SkPaint::kStroke_Style);
+        strokePaint.setStrokeWidth(0.0f);
+
+        for (int y = 0; y < kNumRows; ++y) {
+            for (int x = 0; x < kNumCols; ++x) {
+                SkRect cell = SkRect::MakeXYWH(SkIntToScalar(x*kCellSize),
+                                               SkIntToScalar(y*kCellSize),
+                                               SkIntToScalar(kCellSize),
+                                               SkIntToScalar(kCellSize));
+
+                cell.inset(kPad, kPad);
+                SkPoint clipCenter = SkPoint::Make(cell.centerX() - kClipOffset,
+                                                   cell.centerY() + kClipOffset);
+
+                SkScalar curSize = kCellSize * fFraction;
+
+                // The goal is to replace this clipped draw (which clips the 
+                // shadow) with a draw using the geometric clip
+                if (fDrawWithGaussianEdge) {
+                    canvas->save();
+                          (*clips[x])(canvas, clipCenter, curSize);
+                          (*draws[y])(canvas, cell, false);
+                    canvas->restore();
+                }
+
+                SkPath drawnPath = (*draws[y])(canvas, cell, true);
+
+                if (!fDrawWithGaussianEdge) {
+                    SkPath clippedPath = (*geometricClips[x])(clipCenter, curSize, drawnPath);
+                    SkASSERT(clippedPath.isConvex());
+
+                    SkPaint blurPaint;
+                    blurPaint.setAntiAlias(true);
+                    blurPaint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle, 3.0f));
+                    canvas->drawPath(clippedPath, blurPaint);
+                }
+            }
+        }
+    }
+
+    bool onHandleKey(SkUnichar uni) override {
+        switch (uni) {
+            case 'C':
+                fDrawWithGaussianEdge = !fDrawWithGaussianEdge;
+                return true;
+        }        
+    
+        return false;
+    }
+
+    bool onAnimate(const SkAnimTimer& timer) override {
+        fFraction = timer.pingPong(kPeriod, 0.0f, 0.0f, 1.0f);
+        return true;
+    }
+
+private:
+    SkScalar fFraction;
+    bool     fDrawWithGaussianEdge;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return new RevealGM;)
+}