Hal Canary | 8800042 | 2020-01-15 11:51:12 -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_ANIMATED(SkPath_cubicTo_example_parametric_animated, 512, 512, false, 0, 3) { |
| 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 | // a simple mathematical definition of cubic curve. |
| 22 | // There are faster ways to calculate this. |
| 23 | float s = 1 - t; |
| 24 | return {(s * s * s * p0.x()) + |
| 25 | (3 * s * s * t * p1.x()) + |
| 26 | (3 * s * t * t * p2.x()) + |
| 27 | (t * t * t * p3.x()), |
| 28 | (s * s * s * p0.y()) + |
| 29 | (3 * s * s * t * p1.y()) + |
| 30 | (3 * s * t * t * p2.y()) + |
| 31 | (t * t * t * p3.y())}; |
| 32 | } |
| 33 | |
| 34 | static SkPoint interpolate(SkPoint a, SkPoint b, float t) { |
| 35 | return {SkScalarInterp(a.x(), b.x(), t), |
| 36 | SkScalarInterp(a.y(), b.y(), t)}; |
| 37 | } |
| 38 | |
| 39 | void draw(SkCanvas* canvas) { |
| 40 | canvas->clear(SkColorSetARGB(255,255,255,255)); |
| 41 | |
| 42 | SkPoint a{136, 64}; |
| 43 | SkPoint b{448, 448}; |
| 44 | SkPoint c{64, 448}; |
| 45 | SkPoint d{376, 64}; |
| 46 | |
| 47 | SkPoint ab = interpolate(a, b, frame); |
| 48 | SkPoint bc = interpolate(b, c, frame); |
| 49 | SkPoint cd = interpolate(c, d, frame); |
| 50 | SkPoint abc = interpolate(ab, bc, frame); |
| 51 | SkPoint bcd = interpolate(bc, cd, frame); |
| 52 | |
| 53 | SkPaint paint; |
| 54 | paint.setAntiAlias(true); |
| 55 | paint.setStyle(SkPaint::kStroke_Style); |
| 56 | paint.setStrokeWidth(1); |
| 57 | |
| 58 | canvas->drawLine(ab, bc, paint); |
| 59 | canvas->drawLine(bc, cd, paint); |
| 60 | canvas->drawLine(abc, bcd, paint); |
| 61 | |
| 62 | paint.setStrokeWidth(3); |
| 63 | canvas->drawLine(a, b, paint); |
| 64 | canvas->drawLine(b, c, paint); |
| 65 | canvas->drawLine(c, d, paint); |
| 66 | |
| 67 | paint.setStrokeWidth(5); |
| 68 | paint.setColor(SkColorSetARGB(255, 0, 0, 255)); |
| 69 | SkPath cubicCurve; |
| 70 | cubicCurve.moveTo(a); |
| 71 | cubicCurve.cubicTo(b, c, d); |
| 72 | canvas->drawPath(cubicCurve, paint); |
| 73 | |
| 74 | SkFont font(nullptr, 32); |
| 75 | SkPaint textPaint; |
| 76 | textPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); |
| 77 | textPaint.setAntiAlias(true); |
| 78 | sk_sp<SkFontMgr> mgr(SkFontMgr::RefDefault()); |
| 79 | sk_sp<SkTypeface> face(mgr->matchFamilyStyle("DejaVu Sans Mono", SkFontStyle())); |
| 80 | canvas->drawString("a", a.x(), a.y(), font, textPaint); |
| 81 | canvas->drawString("b", b.x(), b.y(), font, textPaint); |
| 82 | canvas->drawString("c", c.x()-20, c.y(), font, textPaint); |
| 83 | canvas->drawString("d", d.x(), d.y(), font, textPaint); |
| 84 | SkString msg = SkStringPrintf("%.4f", frame); |
| 85 | textPaint.setColor(SkColorSetARGB(255, 204, 204, 204)); |
| 86 | canvas->drawString(msg.c_str(), 4, 36, font, textPaint); |
| 87 | |
| 88 | SkPaint pointPaint; |
| 89 | pointPaint.setAntiAlias(true); |
| 90 | pointPaint.setStrokeWidth(8); |
| 91 | pointPaint.setStrokeCap(SkPaint::kRound_Cap); |
| 92 | |
| 93 | pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0)); |
| 94 | canvas->drawPoint(interpolate(abc, bcd, frame), pointPaint); |
| 95 | |
| 96 | pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); |
| 97 | pointPaint.setStrokeWidth(7); |
| 98 | canvas->drawPoint(cubic(a, b, c, d, frame), pointPaint); |
| 99 | } |
| 100 | } // END FIDDLE |