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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(SkPath_cubicTo_example_parametric, 512, 512, false, 0) { /* If the starting point is (x0, y0), then this curve is defined as the paramentric curve as `t` goes from 0 to 1: s := 1 - t x := (s * s * s * x0) + (3 * s * s * t * x1) + (3 * s * t * t * x2) + (t * t * t * x3) y := (s * s * s * y0) + (3 * s * s * t * y1) + (3 * s * t * t * y2) + (t * t * t * y3) */ SkPoint cubic(SkPoint p0, SkPoint p1, SkPoint p2, SkPoint p3, float t) { float s = 1 - t; return {(s * s * s * p0.x()) + (3 * s * s * t * p1.x()) + (3 * s * t * t * p2.x()) + (t * t * t * p3.x()), (s * s * s * p0.y()) + (3 * s * s * t * p1.y()) + (3 * s * t * t * p2.y()) + (t * t * t * p3.y())}; } void draw(SkCanvas* canvas) { canvas->clear(SkColorSetARGB(255, 255, 255, 255)); SkFont font(nullptr, 32); SkPaint paint; paint.setAntiAlias(true); paint.setStyle(SkPaint::kStroke_Style); paint.setStrokeWidth(5); SkPoint a{136, 64}; SkPoint b{448, 448}; SkPoint c{64, 448}; SkPoint d{376, 64}; SkPath threeSegments; threeSegments.moveTo(a); threeSegments.lineTo(b); threeSegments.lineTo(c); threeSegments.lineTo(d); canvas->drawPath(threeSegments, paint); paint.setColor(SkColorSetARGB(255, 0, 0, 255)); SkPath cubicCurve; cubicCurve.moveTo(a); cubicCurve.cubicTo(b, c, d); canvas->drawPath(cubicCurve, paint); SkPaint textPaint; textPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); textPaint.setAntiAlias(true); canvas->drawString("a", a.x(), a.y(), font, textPaint); canvas->drawString("b", b.x(), b.y(), font, textPaint); canvas->drawString("c", c.x() - 20, c.y(), font, textPaint); canvas->drawString("d", d.x(), d.y(), font, textPaint); SkPaint pointPaint; pointPaint.setAntiAlias(true); pointPaint.setStrokeWidth(8); pointPaint.setStrokeCap(SkPaint::kRound_Cap); pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); const int N = 16; for (int i = 0; i <= N; ++i) { SkPoint p = cubic(a, b, c, d, (float)i / N); canvas->drawPoint(p.x(), p.y(), pointPaint); } pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0)); } } // END FIDDLE