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