xref: /third_party/skia/docs/examples/SkPath_cubicTo_example.cpp

// Copyright 2020 Google LLC.
// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
#include "tools/fiddle/examples.h"
REG_FIDDLE(SkPath_cubicTo_example, 512, 512, false, 0) {
/*
        If the starting point is (x0, y0), then this curve is defined as the
        paramentric curve as `t` goes from 0 to 1:
          s := 1 - t
          x := (s * s * s * x0) +
               (3 * s * s * t * x1) +
               (3 * s * t * t * x2) +
               (t * t * t * x3)
          y := (s * s * s * y0) +
               (3 * s * s * t * y1) +
               (3 * s * t * t * y2) +
               (t * t * t * y3)

*/
void draw(SkCanvas* canvas) {
    canvas->clear(SkColorSetARGB(255, 255, 255, 255));
    SkFont font(nullptr, 32);

    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeWidth(5);

    SkPoint a{128, 64};
    SkPoint b{448, 448};
    SkPoint c{64, 448};
    SkPoint d{384, 64};

    SkPath threeSegments;
    threeSegments.moveTo(a);
    threeSegments.lineTo(b);
    threeSegments.lineTo(c);
    threeSegments.lineTo(d);

    canvas->drawPath(threeSegments, paint);

    paint.setColor(SkColorSetARGB(255, 0, 0, 255));
    SkPath cubicCurve;
    cubicCurve.moveTo(a);
    cubicCurve.cubicTo(b, c, d);
    canvas->drawPath(cubicCurve, paint);

    SkPaint textPaint;
    textPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
    textPaint.setAntiAlias(true);
    canvas->drawString("a", a.x(), a.y(), font, textPaint);
    canvas->drawString("b", b.x(), b.y(), font, textPaint);
    canvas->drawString("c", c.x() - 20, c.y(), font, textPaint);
    canvas->drawString("d", d.x(), d.y(), font, textPaint);
}
}  // END FIDDLE