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_arcto_conic_parametric2, 512, 512, false, 0) { |
| 5 | /** Add a weighted quadratic bezier from the last point, approaching control point |
| 6 | (x1,y1), and ending at (x2,y2). If no moveTo() call has been made for |
| 7 | this contour, the first point is automatically set to (0,0). |
| 8 | If the starting point is (x0, y0), then this curve is defined as the |
| 9 | paramentric curve as `t` goes from 0 to 1: |
| 10 | s := 1 - t |
| 11 | x := ((s * s * x0) + (w * 2 * s * t * x1) + (t * t * x2)) / |
| 12 | ((s * s) + (w * 2 * s * t) + (t * t)) |
| 13 | y := ((s * s * y0) + (w * 2 * s * t * y1) + (t * t * y2)) / |
| 14 | ((s * s) + (w * 2 * s * t) + (t * t)) |
| 15 | @param x1 The x-coordinate of the control point on a quadratic curve |
| 16 | @param y1 The y-coordinate of the control point on a quadratic curve |
| 17 | @param x2 The x-coordinate of the end point on a quadratic curve |
| 18 | @param y2 The y-coordinate of the end point on a quadratic curve |
| 19 | @param w The weight of the control point (x1,y1) |
| 20 | */ |
| 21 | |
| 22 | SkPoint conic(SkPoint p0, SkPoint p1, SkPoint p2, float w, float t) { |
| 23 | float s = 1 - t; |
| 24 | return {((s * s * p0.x()) + (2 * s * t * w * p1.x()) + (t * t * p2.x())) / |
| 25 | ((s * s) + (w * 2 * s * t) + (t * t)), |
| 26 | ((s * s * p0.y()) + (2 * s * t * w * p1.y()) + (t * t * p2.y())) / |
| 27 | ((s * s) + (w * 2 * s * t) + (t * t))}; |
| 28 | } |
| 29 | |
| 30 | void draw(SkCanvas* canvas) { |
| 31 | canvas->clear(SkColorSetARGB(255, 255, 255, 255)); |
| 32 | |
| 33 | SkPaint paint; |
| 34 | paint.setAntiAlias(true); |
| 35 | paint.setStyle(SkPaint::kStroke_Style); |
| 36 | paint.setStrokeWidth(1); |
| 37 | |
| 38 | SkPoint center = {256, 256}; |
| 39 | float r = 192; |
| 40 | SkRect oval = {center.x() - r, center.y() - r, center.x() + r, center.y() + r}; |
| 41 | canvas->drawOval(oval, paint); |
| 42 | float startAngle = 15; |
| 43 | float sweepAngle = 75; |
| 44 | |
| 45 | SkPath arc; |
| 46 | arc.arcTo(oval, startAngle, sweepAngle, false); |
| 47 | |
| 48 | SkPaint arcPaint(paint); |
| 49 | arcPaint.setStrokeWidth(5); |
| 50 | arcPaint.setColor(SkColorSetARGB(255, 0, 0, 255)); |
| 51 | canvas->drawPath(arc, arcPaint); |
| 52 | |
| 53 | SkPaint pointPaint; |
| 54 | pointPaint.setAntiAlias(true); |
| 55 | pointPaint.setStrokeWidth(8); |
| 56 | pointPaint.setStrokeCap(SkPaint::kRound_Cap); |
| 57 | pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0)); |
| 58 | |
| 59 | float finalAngle = startAngle + sweepAngle; |
| 60 | float middleAngle = startAngle + 0.5f * sweepAngle; |
| 61 | float weight = cos(SkDegreesToRadians(sweepAngle) / 2); |
| 62 | SkPoint p0 = {r * SkScalarCos(SkDegreesToRadians(startAngle)), |
| 63 | r * SkScalarSin(SkDegreesToRadians(startAngle))}; |
| 64 | float d = r / weight; |
| 65 | SkPoint p1 = {d * SkScalarCos(SkDegreesToRadians(middleAngle)), |
| 66 | d * SkScalarSin(SkDegreesToRadians(middleAngle))}; |
| 67 | SkPoint p2 = {r * SkScalarCos(SkDegreesToRadians(finalAngle)), |
| 68 | r * SkScalarSin(SkDegreesToRadians(finalAngle))}; |
| 69 | p0 += center; |
| 70 | p1 += center; |
| 71 | p2 += center; |
| 72 | |
| 73 | canvas->drawLine(p0.x(), p0.y(), p1.x(), p1.y(), paint); |
| 74 | canvas->drawLine(p1.x(), p1.y(), p2.x(), p2.y(), paint); |
| 75 | |
| 76 | const int N = 16; |
| 77 | for (int i = 0; i <= N; ++i) { |
| 78 | SkPoint p = conic(p0, p1, p2, weight, (float)i / N); |
| 79 | canvas->drawPoint(p.x(), p.y(), pointPaint); |
| 80 | } |
| 81 | pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0)); |
| 82 | canvas->drawPoint(p0.x(), p0.y(), pointPaint); |
| 83 | canvas->drawPoint(p1.x(), p1.y(), pointPaint); |
| 84 | canvas->drawPoint(p2.x(), p2.y(), pointPaint); |
| 85 | |
| 86 | SkPath weightedQuadratic; |
| 87 | weightedQuadratic.moveTo(p0); |
| 88 | weightedQuadratic.conicTo(p1, p2, weight); |
| 89 | paint.setColor(SK_ColorYELLOW); |
| 90 | paint.setStrokeWidth(2.5); |
| 91 | canvas->drawPath(weightedQuadratic, paint); |
| 92 | } |
| 93 | } // END FIDDLE |