1// Copyright 2020 Google LLC.
2// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
3#include "tools/fiddle/examples.h"
4REG_FIDDLE(SkPath_cubicTo_example_parametric, 512, 512, false, 0) {
5/*
6        If the starting point is (x0, y0), then this curve is defined as the
7        paramentric curve as `t` goes from 0 to 1:
8          s := 1 - t
9          x := (s * s * s * x0) +
10               (3 * s * s * t * x1) +
11               (3 * s * t * t * x2) +
12               (t * t * t * x3)
13          y := (s * s * s * y0) +
14               (3 * s * s * t * y1) +
15               (3 * s * t * t * y2) +
16               (t * t * t * y3)
17
18*/
19
20SkPoint cubic(SkPoint p0, SkPoint p1, SkPoint p2, SkPoint p3, float t) {
21    float s = 1 - t;
22    return {(s * s * s * p0.x()) + (3 * s * s * t * p1.x()) + (3 * s * t * t * p2.x()) +
23                    (t * t * t * p3.x()),
24            (s * s * s * p0.y()) + (3 * s * s * t * p1.y()) + (3 * s * t * t * p2.y()) +
25                    (t * t * t * p3.y())};
26}
27
28void draw(SkCanvas* canvas) {
29    canvas->clear(SkColorSetARGB(255, 255, 255, 255));
30    SkFont font(nullptr, 32);
31
32    SkPaint paint;
33    paint.setAntiAlias(true);
34    paint.setStyle(SkPaint::kStroke_Style);
35    paint.setStrokeWidth(5);
36
37    SkPoint a{136, 64};
38    SkPoint b{448, 448};
39    SkPoint c{64, 448};
40    SkPoint d{376, 64};
41
42    SkPath threeSegments;
43    threeSegments.moveTo(a);
44    threeSegments.lineTo(b);
45    threeSegments.lineTo(c);
46    threeSegments.lineTo(d);
47
48    canvas->drawPath(threeSegments, paint);
49
50    paint.setColor(SkColorSetARGB(255, 0, 0, 255));
51    SkPath cubicCurve;
52    cubicCurve.moveTo(a);
53    cubicCurve.cubicTo(b, c, d);
54    canvas->drawPath(cubicCurve, paint);
55
56    SkPaint textPaint;
57    textPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
58    textPaint.setAntiAlias(true);
59    canvas->drawString("a", a.x(), a.y(), font, textPaint);
60    canvas->drawString("b", b.x(), b.y(), font, textPaint);
61    canvas->drawString("c", c.x() - 20, c.y(), font, textPaint);
62    canvas->drawString("d", d.x(), d.y(), font, textPaint);
63
64    SkPaint pointPaint;
65    pointPaint.setAntiAlias(true);
66    pointPaint.setStrokeWidth(8);
67    pointPaint.setStrokeCap(SkPaint::kRound_Cap);
68    pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
69    const int N = 16;
70    for (int i = 0; i <= N; ++i) {
71        SkPoint p = cubic(a, b, c, d, (float)i / N);
72        canvas->drawPoint(p.x(), p.y(), pointPaint);
73    }
74    pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0));
75}
76}  // END FIDDLE
77