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_ANIMATED(SkPath_cubicTo_example_parametric_animated, 512, 512, false, 0, 3) {
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    // a simple mathematical definition of cubic curve.
22    // There are faster ways to calculate this.
23    float s = 1 - t;
24    return {(s * s * s * p0.x()) +
25            (3 * s * s * t * p1.x()) +
26            (3 * s * t * t * p2.x()) +
27            (t * t * t * p3.x()),
28            (s * s * s * p0.y()) +
29            (3 * s * s * t * p1.y()) +
30            (3 * s * t * t * p2.y()) +
31            (t * t * t * p3.y())};
32}
33
34static SkPoint interpolate(SkPoint a, SkPoint b, float t) {
35   return {SkScalarInterp(a.x(), b.x(), t),
36           SkScalarInterp(a.y(), b.y(), t)};
37}
38
39void draw(SkCanvas* canvas) {
40    canvas->clear(SkColorSetARGB(255,255,255,255));
41
42    SkPoint a{136,  64};
43    SkPoint b{448, 448};
44    SkPoint c{64,  448};
45    SkPoint d{376, 64};
46
47    SkPoint ab = interpolate(a, b, frame);
48    SkPoint bc = interpolate(b, c, frame);
49    SkPoint cd = interpolate(c, d, frame);
50    SkPoint abc = interpolate(ab, bc, frame);
51    SkPoint bcd = interpolate(bc, cd, frame);
52
53    SkPaint paint;
54    paint.setAntiAlias(true);
55    paint.setStyle(SkPaint::kStroke_Style);
56    paint.setStrokeWidth(1);
57
58    canvas->drawLine(ab, bc, paint);
59    canvas->drawLine(bc, cd, paint);
60    canvas->drawLine(abc, bcd, paint);
61
62    paint.setStrokeWidth(3);
63    canvas->drawLine(a, b, paint);
64    canvas->drawLine(b, c, paint);
65    canvas->drawLine(c, d, paint);
66
67    paint.setStrokeWidth(5);
68    paint.setColor(SkColorSetARGB(255, 0, 0, 255));
69    SkPath cubicCurve;
70    cubicCurve.moveTo(a);
71    cubicCurve.cubicTo(b, c, d);
72    canvas->drawPath(cubicCurve, paint);
73
74    SkFont font(nullptr, 32);
75    SkPaint textPaint;
76    textPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
77    textPaint.setAntiAlias(true);
78    sk_sp<SkFontMgr> mgr(SkFontMgr::RefDefault());
79    sk_sp<SkTypeface> face(mgr->matchFamilyStyle("DejaVu Sans Mono", SkFontStyle()));
80    canvas->drawString("a", a.x(),    a.y(), font, textPaint);
81    canvas->drawString("b", b.x(),    b.y(), font, textPaint);
82    canvas->drawString("c", c.x()-20, c.y(), font, textPaint);
83    canvas->drawString("d", d.x(),    d.y(), font, textPaint);
84    SkString msg = SkStringPrintf("%.4f", frame);
85    textPaint.setColor(SkColorSetARGB(255, 204, 204, 204));
86    canvas->drawString(msg.c_str(), 4, 36, font, textPaint);
87
88    SkPaint pointPaint;
89    pointPaint.setAntiAlias(true);
90    pointPaint.setStrokeWidth(8);
91    pointPaint.setStrokeCap(SkPaint::kRound_Cap);
92
93    pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0));
94    canvas->drawPoint(interpolate(abc, bcd, frame), pointPaint);
95
96    pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
97    pointPaint.setStrokeWidth(7);
98    canvas->drawPoint(cubic(a, b, c, d, frame), pointPaint);
99}
100}  // END FIDDLE
101