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_arcto_conic_parametric, 512, 512, false, 0) {
5SkPoint conic(SkPoint p0, SkPoint p1, SkPoint p2, float w, float t) {
6    float s = 1 - t;
7    return {((s * s * p0.x()) + (2 * s * t * w * p1.x()) + (t * t * p2.x())) /
8                    ((s * s) + (w * 2 * s * t) + (t * t)),
9            ((s * s * p0.y()) + (2 * s * t * w * p1.y()) + (t * t * p2.y())) /
10                    ((s * s) + (w * 2 * s * t) + (t * t))};
11}
12
13void draw(SkCanvas* canvas) {
14    canvas->clear(SkColorSetARGB(255, 255, 255, 255));
15
16    SkPaint paint;
17    paint.setAntiAlias(true);
18    paint.setStyle(SkPaint::kStroke_Style);
19    paint.setStrokeWidth(2.5);
20
21    SkPoint center = {256, 256};
22    float r = 192;
23    SkRect oval = {center.x() - r, center.y() - r, center.x() + r, center.y() + r};
24    canvas->drawOval(oval, paint);
25    float startAngle = 0;
26    float sweepAngle = 179;
27
28    SkPath arc;
29    arc.arcTo(oval, startAngle, sweepAngle, false);
30
31    paint.setStrokeWidth(5);
32    paint.setColor(SkColorSetARGB(255, 0, 0, 255));
33    canvas->drawPath(arc, paint);
34
35    SkPaint pointPaint;
36    pointPaint.setAntiAlias(true);
37    pointPaint.setStrokeWidth(8);
38    pointPaint.setStrokeCap(SkPaint::kRound_Cap);
39    pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
40
41    float finalAngle = startAngle + sweepAngle;
42    float middleAngle = startAngle + 0.5f * sweepAngle;
43    float weight = cos(SkDegreesToRadians(sweepAngle) / 2);
44    SkPoint p0 = {r * SkScalarCos(SkDegreesToRadians(startAngle)),
45                  r * SkScalarSin(SkDegreesToRadians(startAngle))};
46    float d = r / weight;
47    SkPoint p1 = {d * SkScalarCos(SkDegreesToRadians(middleAngle)),
48                  d * SkScalarSin(SkDegreesToRadians(middleAngle))};
49    SkPoint p2 = {r * SkScalarCos(SkDegreesToRadians(finalAngle)),
50                  r * SkScalarSin(SkDegreesToRadians(finalAngle))};
51    p0 += center;
52    p1 += center;
53    p2 += center;
54
55    const int N = 8;
56    for (int i = 0; i <= N; ++i) {
57        SkPoint p = conic(p0, p1, p2, weight, (float)i / N);
58        canvas->drawPoint(p.x(), p.y(), pointPaint);
59    }
60    pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0));
61    canvas->drawPoint(p0.x(), p0.y(), pointPaint);
62    canvas->drawPoint(p1.x(), p1.y(), pointPaint);
63    canvas->drawPoint(p2.x(), p2.y(), pointPaint);
64
65    SkPath weightedQuadratic;
66    weightedQuadratic.moveTo(p0);
67    weightedQuadratic.conicTo(p1, p2, weight);
68    paint.setColor(SK_ColorCYAN);
69    paint.setStrokeWidth(1);
70    canvas->drawPath(weightedQuadratic, paint);
71}
72}  // END FIDDLE
73