[SVGDom] SVGPong sample app

samplecode/SampleSVGPong.cpp

Index: samplecode/SampleSVGPong.cpp
diff --git a/samplecode/SampleSVGPong.cpp b/samplecode/SampleSVGPong.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..be107b64dcbe9515c75b3cc0efce82ce0ca66855
--- /dev/null
+++ b/samplecode/SampleSVGPong.cpp
@@ -0,0 +1,286 @@
+/*
+ * 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 "SkAnimTimer.h"
+#include "SkColor.h"
+#include "SkRandom.h"
+#include "SkRRect.h"
+#include "SkSVGDOM.h"
+#include "SkSVGG.h"
+#include "SkSVGPath.h"
+#include "SkSVGRect.h"
+#include "SkSVGSVG.h"
+
+namespace {
+
+static const SkRect kBounds     = SkRect::MakeLTRB(0.1f, 0.1f, 0.9f, 0.9f);
+static const SkSize kPaddleSize = SkSize::Make(0.03f, 0.1f);
+static const SkScalar kBallSize = 0.04f;
+static const SkScalar kShadowOpacity       = 0.40f;
+static const SkScalar kShadowParallax      = 0.04f;
+static const SkScalar kBackgroundStroke    = 0.01f;
+static const uint32_t kBackgroundDashCount = 20;
+
+static const SkScalar kBallSpeedMax  = 0.0020f;
+static const SkScalar kBallSpeedMin  = 0.0005f;
+static const SkScalar kBallSpeedFuzz = 0.0002f;
+
+static const SkScalar kTimeScaleMin = 0.0f;
+static const SkScalar kTimeScaleMax = 5.0f;
+
+// Box the value within [min, max), by applying infinite reflection on the interval endpoints.
+SkScalar box_reflect(SkScalar v, SkScalar min, SkScalar max) {
+    const SkScalar intervalLen = max - min;
+    SkASSERT(intervalLen > 0);
+
+    // f(v) is periodic in 2 * intervalLen: one normal progression + one reflection
+    const SkScalar P = intervalLen * 2;
+    // relative to P origin
+    const SkScalar vP = v - min;
+    // map to [0, P)
+    const SkScalar vMod = (vP < 0) ? P - SkScalarMod(-vP, P) : SkScalarMod(vP, P);
+    // reflect if needed, to map to [0, intervalLen)
+    const SkScalar vInterval = vMod < intervalLen ? vMod : P - vMod;
+    // finally, reposition relative to min
+    return vInterval + min;
+}
+
+// Compute <t, y> for the trajectory intersection with the next vertical edge.
+std::tuple<SkScalar, SkScalar> find_yintercept(const SkPoint& pos, const SkVector& spd,
+                                               const SkRect& box) {
+    const SkScalar edge = spd.fX > 0 ? box.fRight : box.fLeft;
+    const SkScalar    t = (edge - pos.fX) / spd.fX;
+    SkASSERT(t >= 0);
+    const SkScalar   dY = t * spd.fY;
+
+    return std::make_tuple(t, box_reflect(pos.fY + dY, box.fTop, box.fBottom));
+}
+
+sk_sp<SkSVGRect> make_svg_rrect(const SkRRect& rrect) {
+    sk_sp<SkSVGRect> node = SkSVGRect::Make();
+    node->setX(SkSVGLength(rrect.rect().x()));
+    node->setY(SkSVGLength(rrect.rect().y()));
+    node->setWidth(SkSVGLength(rrect.width()));
+    node->setHeight(SkSVGLength(rrect.height()));
+    node->setRx(SkSVGLength(rrect.getSimpleRadii().x()));
+    node->setRy(SkSVGLength(rrect.getSimpleRadii().y()));
+
+    return node;
+}
+
+} // anonymous ns
+
+class SVGPongView final : public SampleView {
+public:
+    SVGPongView() {}
+
+protected:
+    void onOnceBeforeDraw() override {
+        const SkRect fieldBounds = kBounds.makeOutset(kBallSize / 2, kBallSize / 2);
+        const SkRRect ball = SkRRect::MakeOval(SkRect::MakeWH(kBallSize, kBallSize));
+        const SkRRect paddle = SkRRect::MakeRectXY(SkRect::MakeWH(kPaddleSize.width(),
+                                                                  kPaddleSize.height()),
+                                                   kPaddleSize.width() / 2,
+                                                   kPaddleSize.width() / 2);
+        fBall.initialize(ball,
+                         SK_ColorGREEN,
+                         SkPoint::Make(kBounds.centerX(), kBounds.centerY()),
+                         SkVector::Make(fRand.nextRangeScalar(kBallSpeedMin, kBallSpeedMax),
+                                        fRand.nextRangeScalar(kBallSpeedMin, kBallSpeedMax)));
+        fPaddle0.initialize(paddle,
+                            SK_ColorBLUE,
+                            SkPoint::Make(fieldBounds.left() - kPaddleSize.width() / 2,
+                                          fieldBounds.centerY()),
+                            SkVector::Make(0, 0));
+        fPaddle1.initialize(paddle,
+                            SK_ColorRED,
+                            SkPoint::Make(fieldBounds.right() + kPaddleSize.width() / 2,
+                                          fieldBounds.centerY()),
+                            SkVector::Make(0, 0));
+
+        // Background decoration.
+        SkPath bgPath;
+        bgPath.moveTo(kBounds.left() , fieldBounds.top());
+        bgPath.lineTo(kBounds.right(), fieldBounds.top());
+        bgPath.moveTo(kBounds.left() , fieldBounds.bottom());
+        bgPath.lineTo(kBounds.right(), fieldBounds.bottom());
+        // TODO: stroke-dash support would come in handy right about now.
+        for (uint32_t i = 0; i < kBackgroundDashCount; ++i) {
+            bgPath.moveTo(kBounds.centerX(),
+                          kBounds.top() + (i + 0.25f) * kBounds.height() / kBackgroundDashCount);
+            bgPath.lineTo(kBounds.centerX(),
+                          kBounds.top() + (i + 0.75f) * kBounds.height() / kBackgroundDashCount);
+        }
+
+        sk_sp<SkSVGPath> bg = SkSVGPath::Make();
+        bg->setPath(bgPath);
+        bg->setFill(SkSVGPaint(SkSVGPaint::Type::kNone));
+        bg->setStroke(SkSVGPaint(SkSVGColorType(SK_ColorBLACK)));
+        bg->setStrokeWidth(SkSVGLength(kBackgroundStroke));
+
+        // Build the SVG DOM tree.
+        sk_sp<SkSVGSVG> root = SkSVGSVG::Make();
+        root->appendChild(std::move(bg));
+        root->appendChild(fPaddle0.shadowNode);
+        root->appendChild(fPaddle1.shadowNode);
+        root->appendChild(fBall.shadowNode);
+        root->appendChild(fPaddle0.objectNode);
+        root->appendChild(fPaddle1.objectNode);
+        root->appendChild(fBall.objectNode);
+
+        // Handle everything in a normalized 1x1 space.
+        root->setViewBox(SkSVGViewBoxType(SkRect::MakeWH(1, 1)));
+
+        fDom = sk_sp<SkSVGDOM>(new SkSVGDOM(SkSize::Make(this->width(), this->height())));
+        fDom->setRoot(std::move(root));
+
+        // Off we go.
+        this->updatePaddleStrategy();
+    }
+
+    bool onQuery(SkEvent* evt) override {
+        if (SampleCode::TitleQ(*evt)) {
+            SampleCode::TitleR(evt, "SVGPong");
+            return true;
+        }
+
+        SkUnichar uni;
+        if (SampleCode::CharQ(*evt, &uni)) {
+            switch (uni) {
+                case '[':
+                    fTimeScale = SkTPin(fTimeScale - 0.1f, kTimeScaleMin, kTimeScaleMax);
+                    return true;
+                case ']':
+                    fTimeScale = SkTPin(fTimeScale + 0.1f, kTimeScaleMin, kTimeScaleMax);
+                    return true;
+                default:
+                    break;
+            }
+        }
+        return this->INHERITED::onQuery(evt);
+    }
+
+    void onSizeChange() override {
+        if (fDom) {
+            fDom->setContainerSize(SkSize::Make(this->width(), this->height()));
+        }
+
+        this->INHERITED::onSizeChange();
+    }
+
+    void onDrawContent(SkCanvas* canvas) override {
+        fDom->render(canvas);
+    }
+
+    bool onAnimate(const SkAnimTimer& timer) override {
+        SkScalar dt = (timer.msec() - fLastTick) * fTimeScale;
+        fLastTick = timer.msec();
+
+        fPaddle0.posTick(dt);
+        fPaddle1.posTick(dt);
+        fBall.posTick(dt);
+
+        this->enforceConstraints();
+
+        fPaddle0.updateDom();
+        fPaddle1.updateDom();
+        fBall.updateDom();
+
+        return true;
+    }
+
+private:
+    struct Object {
+        void initialize(const SkRRect& rrect, SkColor color,
+                        const SkPoint& p, const SkVector& s) {
+            objectNode = make_svg_rrect(rrect);
+            objectNode->setFill(SkSVGPaint(SkSVGColorType(color)));
+
+            shadowNode = make_svg_rrect(rrect);
+            shadowNode->setFillOpacity(SkSVGNumberType(kShadowOpacity));
+
+            pos = p;
+            spd = s;
+            size = SkSize::Make(rrect.width(), rrect.height());
+        }
+
+        void posTick(SkScalar dt) {
+            pos += spd * dt;
+        }
+
+        void updateDom() {
+            const SkPoint corner = pos - SkPoint::Make(size.width() / 2, size.height() / 2);
+            objectNode->setX(SkSVGLength(corner.x()));
+            objectNode->setY(SkSVGLength(corner.y()));
+
+            // Simulate parallax shadow for a centered light source.
+            SkPoint shadowOffset = pos - SkPoint::Make(kBounds.centerX(), kBounds.centerY());
+            shadowOffset.scale(kShadowParallax);
+            const SkPoint shadowCorner = corner + shadowOffset;
+
+            shadowNode->setX(SkSVGLength(shadowCorner.x()));
+            shadowNode->setY(SkSVGLength(shadowCorner.y()));
+        }
+
+        sk_sp<SkSVGRect> objectNode;
+        sk_sp<SkSVGRect> shadowNode;
+        SkPoint          pos;
+        SkVector         spd;
+        SkSize           size;
+    };
+
+    void enforceConstraints() {
+        // Perfect vertical reflection.
+        if (fBall.pos.fY < kBounds.fTop || fBall.pos.fY >= kBounds.fBottom) {
+            fBall.spd.fY = -fBall.spd.fY;
+            fBall.pos.fY = box_reflect(fBall.pos.fY, kBounds.fTop, kBounds.fBottom);
+        }
+
+        // Horizontal bounce - introduces a speed fuzz.
+        if (fBall.pos.fX < kBounds.fLeft || fBall.pos.fX >= kBounds.fRight) {
+            fBall.spd.fX = this->fuzzBallSpeed(-fBall.spd.fX);
+            fBall.spd.fY = this->fuzzBallSpeed(fBall.spd.fY);
+            fBall.pos.fX = box_reflect(fBall.pos.fX, kBounds.fLeft, kBounds.fRight);
+            this->updatePaddleStrategy();
+        }
+    }
+
+    SkScalar fuzzBallSpeed(SkScalar spd) {
+        // The speed limits are absolute values.
+        const SkScalar   sign = spd >= 0 ? 1.0f : -1.0f;
+        const SkScalar fuzzed = fabs(spd) + fRand.nextRangeScalar(-kBallSpeedFuzz, kBallSpeedFuzz);
+
+        return sign * SkTPin(fuzzed, kBallSpeedMin, kBallSpeedMax);
+    }
+
+    void updatePaddleStrategy() {
+        Object* pitcher = fBall.spd.fX > 0 ? &fPaddle0 : &fPaddle1;
+        Object* catcher = fBall.spd.fX > 0 ? &fPaddle1 : &fPaddle0;
+
+        SkScalar t, yIntercept;
+        std::tie(t, yIntercept) = find_yintercept(fBall.pos, fBall.spd, kBounds);
+
+        // The pitcher aims for a neutral/centered position.
+        pitcher->spd.fY = (kBounds.centerY() - pitcher->pos.fY) / t;
+
+        // The catcher goes for the ball.  Duh.
+        catcher->spd.fY = (yIntercept - catcher->pos.fY) / t;
+    }
+
+    sk_sp<SkSVGDOM> fDom;
+    Object          fPaddle0, fPaddle1, fBall;
+    SkRandom        fRand;
+
+    SkMSec          fLastTick  = 0;
+    SkScalar        fTimeScale = 1.0f;
+
+    typedef SampleView INHERITED;
+};
+
+static SkView* SVGPongFactory() { return new SVGPongView; }
+static SkViewRegister reg(SVGPongFactory);