Hal Canary | 6c8422c | 2020-01-10 15:22:09 -0500 | [diff] [blame] | 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(SkPath_cubicTo_example_parametric, 512, 512, false, 0) { |
| 5 | /* |
| 6 | If the starting point is (x0, y0), then this curve is defined as the |
| 7 | paramentric curve as `t` goes from 0 to 1: |
| 8 | s := 1 - t |
| 9 | x := (s * s * s * x0) + |
| 10 | (3 * s * s * t * x1) + |
| 11 | (3 * s * t * t * x2) + |
| 12 | (t * t * t * x3) |
| 13 | y := (s * s * s * y0) + |
| 14 | (3 * s * s * t * y1) + |
| 15 | (3 * s * t * t * y2) + |
| 16 | (t * t * t * y3) |
| 17 | |
| 18 | */ |
| 19 | |
| 20 | SkPoint cubic(SkPoint p0, SkPoint p1, SkPoint p2, SkPoint p3, float t) { |
| 21 | float s = 1 - t; |
| 22 | return {(s * s * s * p0.x()) + (3 * s * s * t * p1.x()) + (3 * s * t * t * p2.x()) + |
| 23 | (t * t * t * p3.x()), |
| 24 | (s * s * s * p0.y()) + (3 * s * s * t * p1.y()) + (3 * s * t * t * p2.y()) + |
| 25 | (t * t * t * p3.y())}; |
| 26 | } |
| 27 | |
| 28 | void draw(SkCanvas* canvas) { |
| 29 | canvas->clear(SkColorSetARGB(255, 255, 255, 255)); |
| 30 | SkFont font(nullptr, 32); |
| 31 | |
| 32 | SkPaint paint; |
| 33 | paint.setAntiAlias(true); |
| 34 | paint.setStyle(SkPaint::kStroke_Style); |
| 35 | paint.setStrokeWidth(5); |
| 36 | |
| 37 | SkPoint a{136, 64}; |
| 38 | SkPoint b{448, 448}; |
| 39 | SkPoint c{64, 448}; |
| 40 | SkPoint d{376, 64}; |
| 41 | |
| 42 | SkPath threeSegments; |
| 43 | threeSegments.moveTo(a); |
| 44 | threeSegments.lineTo(b); |
| 45 | threeSegments.lineTo(c); |
| 46 | threeSegments.lineTo(d); |
| 47 | |
| 48 | canvas->drawPath(threeSegments, paint); |
| 49 | |
| 50 | paint.setColor(SkColorSetARGB(255, 0, 0, 255)); |
| 51 | SkPath cubicCurve; |
| 52 | cubicCurve.moveTo(a); |
| 53 | cubicCurve.cubicTo(b, c, d); |
| 54 | canvas->drawPath(cubicCurve, paint); |
| 55 | |
| 56 | SkPaint textPaint; |
| 57 | textPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); |
| 58 | textPaint.setAntiAlias(true); |
| 59 | canvas->drawString("a", a.x(), a.y(), font, textPaint); |
| 60 | canvas->drawString("b", b.x(), b.y(), font, textPaint); |
| 61 | canvas->drawString("c", c.x() - 20, c.y(), font, textPaint); |
| 62 | canvas->drawString("d", d.x(), d.y(), font, textPaint); |
| 63 | |
| 64 | SkPaint pointPaint; |
| 65 | pointPaint.setAntiAlias(true); |
| 66 | pointPaint.setStrokeWidth(8); |
| 67 | pointPaint.setStrokeCap(SkPaint::kRound_Cap); |
| 68 | pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); |
| 69 | const int N = 16; |
| 70 | for (int i = 0; i <= N; ++i) { |
| 71 | SkPoint p = cubic(a, b, c, d, (float)i / N); |
| 72 | canvas->drawPoint(p.x(), p.y(), pointPaint); |
| 73 | } |
| 74 | pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0)); |
| 75 | } |
| 76 | } // END FIDDLE |