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"
4 REG_FIDDLE(SmoothBezierSplineInterpolation, 1024, 1024, false, 0) {
5 // Smooth Bézier Spline Interpolation
6 
MakeCubicSplineInterpolation(const SkPoint * pts,size_t N)7 SkPath 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 
draw(SkCanvas * canvas)62 void 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