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_quadTo_example_parametric, 512, 512, false, 0) {
5SkPoint quad(SkPoint p0, SkPoint p1, SkPoint p2, float t) {
6    float s = 1 - t;
7    return {(s * s * p0.x()) + (2 * s * t * p1.x()) + (t * t * p2.x()),
8            (s * s * p0.y()) + (2 * s * t * p1.y()) + (t * t * p2.y())};
9}
10
11/*
12
13        If the starting point is (x0, y0), then this curve is defined as the
14        paramentric curve as `t` goes from 0 to 1:
15
16          s := 1 - t
17          x := (s * s * x0) + (2 * s * t * x1) + (t * t * x2)
18          y := (s * s * y0) + (2 * s * t * y1) + (t * t * y2)
19
20*/
21
22void draw(SkCanvas* canvas) {
23    canvas->clear(SkColorSetARGB(255, 255, 255, 255));
24
25    SkPaint paint;
26    paint.setAntiAlias(true);
27    paint.setStyle(SkPaint::kStroke_Style);
28    paint.setStrokeWidth(5);
29
30    SkPoint a{100, 100};
31    SkPoint b{200, 400};
32    SkPoint c{300, 100};
33
34    SkPath twoSegments;
35    twoSegments.moveTo(a);
36    twoSegments.lineTo(b);
37    twoSegments.lineTo(c);
38
39    canvas->drawPath(twoSegments, paint);
40
41    paint.setColor(SkColorSetARGB(255, 0, 0, 255));
42    SkPath quadraticCurve;
43    quadraticCurve.moveTo(a);
44    quadraticCurve.quadTo(b, c);
45    canvas->drawPath(quadraticCurve, paint);
46
47    SkFont font(nullptr, 32);
48    SkPaint textPaint;
49    textPaint.setAntiAlias(true);
50    canvas->drawString("a", a.x(), a.y(), font, textPaint);
51    canvas->drawString("b", b.x() + 20, b.y() + 20, font, textPaint);
52    canvas->drawString("c", c.x(), c.y(), font, textPaint);
53
54    SkPaint pointPaint;
55    pointPaint.setAntiAlias(true);
56    pointPaint.setStrokeWidth(8);
57    pointPaint.setStrokeCap(SkPaint::kRound_Cap);
58    pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
59    int N = 15;
60    for (int i = 0; i <= N; ++i) {
61        SkPoint p = quad(a, b, c, (float)i / N);
62        canvas->drawPoint(p.x(), p.y(), pointPaint);
63    }
64}
65}  // END FIDDLE
66