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(SmoothBezierSplineInterpolation, 1024, 1024, false, 0) {
5// Smooth Bézier Spline Interpolation
6
7SkPath MakeCubicSplineInterpolation(const SkPoint* pts, size_t N) {
8    // Code borrowed from https://www.particleincell.com/2012/bezier-splines/
9
10    SkPath path;
11    if (N < 2) {
12        return path;
13    }
14    if (N == 2) {
15        path.moveTo(pts[0]);
16        path.lineTo(pts[1]);
17        return path;
18    }
19    size_t n = N - 1;  // number of segments
20    struct Scratch {
21        SkPoint a, b, c, r, p;
22    };
23    // Can I do this will less allocation?
24    std::unique_ptr<Scratch[]> s(new Scratch[n]);
25    s[0].a = {0, 0};
26    s[0].b = {2, 2};
27    s[0].c = {1, 1};
28    s[0].r = {pts[0].x() + 2 * pts[1].x(), pts[0].y() + 2 * pts[1].y()};
29    for (size_t i = 1; i < n - 1; ++i) {
30        s[i].a = {1, 1};
31        s[i].b = {4, 4};
32        s[i].c = {1, 1};
33        s[i].r = {4 * pts[i].x() + 2 * pts[i + 1].x(), 4 * pts[i].y() + 2 * pts[i + 1].y()};
34    }
35    s[n - 1].a = {2, 2};
36    s[n - 1].b = {7, 7};
37    s[n - 1].c = {0, 0};
38    s[n - 1].r = {8 * pts[n - 1].x() + pts[N - 1].x(), 8 * pts[n - 1].y() + pts[N - 1].y()};
39    for (size_t i = 1; i < n; i++) {
40        float mx = s[i].a.x() / s[i - 1].b.x();
41        float my = s[i].a.y() / s[i - 1].b.y();
42        s[i].b -= {mx * s[i - 1].c.x(), my * s[i - 1].c.y()};
43        s[i].r -= {mx * s[i - 1].r.x(), my * s[i - 1].r.y()};
44    }
45    s[n - 1].p = {s[n - 1].r.x() / s[n - 1].b.x(), s[n - 1].r.y() / s[n - 1].b.y()};
46    for (int i = (int)N - 3; i >= 0; --i) {
47        s[i].p = {(s[i].r.x() - s[i].c.x() * s[i + 1].p.fX) / s[i].b.x(),
48                  (s[i].r.y() - s[i].c.y() * s[i + 1].p.fY) / s[i].b.y()};
49    }
50
51    path.moveTo(pts[0]);
52    for (size_t i = 0; i < n - 1; i++) {
53        SkPoint q = {2 * pts[i + 1].x() - s[i + 1].p.fX, 2 * pts[i + 1].y() - s[i + 1].p.fY};
54        path.cubicTo(s[i].p, q, pts[i + 1]);
55    }
56    SkPoint q = {0.5f * (pts[N - 1].x() + s[n - 1].p.x()),
57                 0.5f * (pts[N - 1].y() + s[n - 1].p.y())};
58    path.cubicTo(s[n - 1].p, q, pts[n]);
59    return path;
60}
61
62void draw(SkCanvas* canvas) {
63    SkPaint p;
64    p.setColor(SK_ColorRED);
65    p.setAntiAlias(true);
66    p.setStyle(SkPaint::kStroke_Style);
67    p.setStrokeWidth(3);
68    p.setStrokeCap(SkPaint::kRound_Cap);
69
70    // randomly generated y values in range [12,1024].
71    SkPoint pts[] = {
72            {62, 511}, {162, 605}, {262, 610}, {362, 402}, {462, 959},
73            {562, 58}, {662, 272}, {762, 99},  {862, 759}, {962, 945},
74    };
75
76    canvas->drawPath(MakeCubicSplineInterpolation(pts, SK_ARRAY_COUNT(pts)), p);
77
78    p.setStrokeWidth(10);
79    p.setColor(SK_ColorBLACK);
80    canvas->drawPoints(SkCanvas::kPoints_PointMode, SK_ARRAY_COUNT(pts), pts, p);
81}
82}  // END FIDDLE
83