samplecode/SampleDegenerateTwoPtRadials.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkCanvas.h"
#include "include/core/SkFont.h"
#include "include/core/SkString.h"
#include "include/effects/SkGradientShader.h"
#include "samplecode/Sample.h"

static void draw_gradient2(SkCanvas* canvas, const SkRect& rect, SkScalar delta) {
    SkColor colors[] = { SK_ColorRED, SK_ColorGREEN, SK_ColorBLUE, SK_ColorMAGENTA };
    SkScalar pos[] = { 0, 0.25f, 0.75f, SK_Scalar1 };

    SkScalar l = rect.fLeft;
    SkScalar t = rect.fTop;
    SkScalar w = rect.width();
    SkScalar h = rect.height();

    SkASSERT(0 == SkScalarMod(w, SK_Scalar1 * 5));

    SkPoint c0 = { l + 2 * w / 5 + delta, t + h / 2 };
    SkPoint c1 = { l + 3 * w / 5, t + h / 2 };
    SkScalar r0 = w / 5;
    SkScalar r1 = 2 * w / 5;
    SkPaint paint;
    paint.setShader(SkGradientShader::MakeTwoPointConical(c0, r0, c1, r1, colors,
                                                          pos, SK_ARRAY_COUNT(pos),
                                                          SkTileMode::kClamp));
    canvas->drawRect(rect, paint);
}


class DegenerateTwoPtRadialsView : public Sample {
public:
    DegenerateTwoPtRadialsView() {
        fTime = 0;
        this->setBGColor(0xFFDDDDDD);
    }

protected:
    SkString name() override { return SkString("DegenerateTwoPtRadials"); }

    void onDrawContent(SkCanvas* canvas) override {
        SkScalar delta = fTime / 15.f;
        int intPart = SkScalarFloorToInt(delta);
        delta = delta - SK_Scalar1 * intPart;
        if (intPart % 2) {
            delta = SK_Scalar1 - delta;
        }
        delta -= SK_ScalarHalf;
        static const int DELTA_SCALE = 500;
        delta /= DELTA_SCALE;

        SkScalar w = SK_Scalar1 * 500;
        SkScalar h = SK_Scalar1 * 500;
        SkScalar l = SK_Scalar1 * 100;
        SkScalar t = SK_Scalar1 * 100;
        draw_gradient2(canvas, SkRect::MakeXYWH(l, t, w, h), delta);
        SkString txt;
        txt.appendf("gap at \"tangent\" pt = %f", SkScalarToFloat(delta));
        canvas->drawString(txt, l + w / 2 + w * DELTA_SCALE * delta, t + h + SK_Scalar1 * 10,
                           SkFont(), SkPaint());
    }

    bool onAnimate(double nanos) override {
        fTime = SkDoubleToScalar(1e-9 * nanos / 15);
        return true;
    }

private:
    SkScalar           fTime;
    using INHERITED = Sample;
};

//////////////////////////////////////////////////////////////////////////////

DEF_SAMPLE( return new DegenerateTwoPtRadialsView(); )