DegenerateTwoPtRadialsSlide.cpp

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/*
 * 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 "tools/fonts/FontToolUtils.h"
#include "tools/viewer/Slide.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, std::size(pos),
                                                          SkTileMode::kClamp));
    canvas->drawRect(rect, paint);
}
 
 
class DegenerateTwoPtRadialsSlide : public Slide {
public:
    DegenerateTwoPtRadialsSlide() { fName = "DegenerateTwoPtRadials"; }
 
    void draw(SkCanvas* canvas) override {
        canvas->clear(0xFFDDDDDD);
        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", delta);
        canvas->drawString(txt,
                           l + w / 2 + w * DELTA_SCALE * delta,
                           t + h + SK_Scalar1 * 10,
                           ToolUtils::DefaultFont(),
                           SkPaint());
    }
 
    bool animate(double nanos) override {
        fTime = SkDoubleToScalar(1e-9 * nanos / 15);
        return true;
    }
 
private:
    SkScalar           fTime;
};
 
//////////////////////////////////////////////////////////////////////////////
 
DEF_SLIDE( return new DegenerateTwoPtRadialsSlide(); )