83 lines
2.8 KiB
C++
83 lines
2.8 KiB
C++
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// Copyright 2020 Google LLC.
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// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
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#include "tools/fiddle/examples.h"
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REG_FIDDLE(SmoothBezierSplineInterpolation, 1024, 1024, false, 0) {
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// Smooth Bézier Spline Interpolation
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SkPath MakeCubicSplineInterpolation(const SkPoint* pts, size_t N) {
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// Code borrowed from https://www.particleincell.com/2012/bezier-splines/
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SkPath path;
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if (N < 2) {
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return path;
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}
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if (N == 2) {
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path.moveTo(pts[0]);
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path.lineTo(pts[1]);
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return path;
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}
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size_t n = N - 1; // number of segments
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struct Scratch {
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SkPoint a, b, c, r, p;
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};
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// Can I do this will less allocation?
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std::unique_ptr<Scratch[]> s(new Scratch[n]);
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s[0].a = {0, 0};
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s[0].b = {2, 2};
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s[0].c = {1, 1};
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s[0].r = {pts[0].x() + 2 * pts[1].x(), pts[0].y() + 2 * pts[1].y()};
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for (size_t i = 1; i < n - 1; ++i) {
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s[i].a = {1, 1};
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s[i].b = {4, 4};
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s[i].c = {1, 1};
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s[i].r = {4 * pts[i].x() + 2 * pts[i + 1].x(), 4 * pts[i].y() + 2 * pts[i + 1].y()};
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}
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s[n - 1].a = {2, 2};
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s[n - 1].b = {7, 7};
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s[n - 1].c = {0, 0};
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s[n - 1].r = {8 * pts[n - 1].x() + pts[N - 1].x(), 8 * pts[n - 1].y() + pts[N - 1].y()};
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for (size_t i = 1; i < n; i++) {
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float mx = s[i].a.x() / s[i - 1].b.x();
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float my = s[i].a.y() / s[i - 1].b.y();
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s[i].b -= {mx * s[i - 1].c.x(), my * s[i - 1].c.y()};
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s[i].r -= {mx * s[i - 1].r.x(), my * s[i - 1].r.y()};
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}
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s[n - 1].p = {s[n - 1].r.x() / s[n - 1].b.x(), s[n - 1].r.y() / s[n - 1].b.y()};
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for (int i = (int)N - 3; i >= 0; --i) {
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s[i].p = {(s[i].r.x() - s[i].c.x() * s[i + 1].p.fX) / s[i].b.x(),
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(s[i].r.y() - s[i].c.y() * s[i + 1].p.fY) / s[i].b.y()};
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}
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path.moveTo(pts[0]);
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for (size_t i = 0; i < n - 1; i++) {
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SkPoint q = {2 * pts[i + 1].x() - s[i + 1].p.fX, 2 * pts[i + 1].y() - s[i + 1].p.fY};
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path.cubicTo(s[i].p, q, pts[i + 1]);
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}
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SkPoint q = {0.5f * (pts[N - 1].x() + s[n - 1].p.x()),
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0.5f * (pts[N - 1].y() + s[n - 1].p.y())};
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path.cubicTo(s[n - 1].p, q, pts[n]);
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return path;
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}
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void draw(SkCanvas* canvas) {
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SkPaint p;
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p.setColor(SK_ColorRED);
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p.setAntiAlias(true);
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p.setStyle(SkPaint::kStroke_Style);
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p.setStrokeWidth(3);
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p.setStrokeCap(SkPaint::kRound_Cap);
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// randomly generated y values in range [12,1024].
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SkPoint pts[] = {
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{62, 511}, {162, 605}, {262, 610}, {362, 402}, {462, 959},
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{562, 58}, {662, 272}, {762, 99}, {862, 759}, {962, 945},
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};
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canvas->drawPath(MakeCubicSplineInterpolation(pts, SK_ARRAY_COUNT(pts)), p);
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p.setStrokeWidth(10);
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p.setColor(SK_ColorBLACK);
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canvas->drawPoints(SkCanvas::kPoints_PointMode, SK_ARRAY_COUNT(pts), pts, p);
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}
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} // END FIDDLE
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