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