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_quadTo_example_parametric_animated, 512, 512, false, 0, 4) {
5 // SkPath_quadTo_example_parametric_animated
6
quad(SkPoint p0,SkPoint p1,SkPoint p2,float t)7 SkPoint quad(SkPoint p0, SkPoint p1, SkPoint p2, float t) {
8 float s = 1 - t;
9 return {(s * s * p0.x()) + (2 * s * t * p1.x()) + (t * t * p2.x()),
10 (s * s * p0.y()) + (2 * s * t * p1.y()) + (t * t * p2.y())};
11 }
12
13 /*
14
15 If the starting point is (x0, y0), then this curve is defined as the
16 paramentric curve as `t` goes from 0 to 1:
17
18 s := 1 - t
19 x := (s * s * x0) + (2 * s * t * x1) + (t * t * x2)
20 y := (s * s * y0) + (2 * s * t * y1) + (t * t * y2)
21
22 */
23
interpolate(SkPoint a,SkPoint b,float t)24 static SkPoint interpolate(SkPoint a, SkPoint b, float t) {
25 return {SkScalarInterp(a.x(), b.x(), t),
26 SkScalarInterp(a.y(), b.y(), t)};
27 }
28
draw_line(SkCanvas * canvas,SkPoint p0,SkPoint p1,const SkPaint & paint)29 static void draw_line(SkCanvas* canvas, SkPoint p0, SkPoint p1, const SkPaint& paint) {
30 canvas->drawLine(p0.x(), p0.y(), p1.x(), p1.y(), paint);
31 }
32
draw_point(SkCanvas * canvas,SkPoint p,const SkPaint & paint)33 static void draw_point(SkCanvas* canvas, SkPoint p, const SkPaint& paint) {
34 canvas->drawPoint(p.x(), p.y(), paint);
35 }
36
draw(SkCanvas * canvas)37 void draw(SkCanvas* canvas) {
38 canvas->clear(SkColorSetARGB(255,255,255,255));
39
40 SkPaint paint;
41 paint.setAntiAlias(true);
42 paint.setStyle(SkPaint::kStroke_Style);
43 paint.setStrokeWidth(5);
44
45 SkPoint a{10, 100};
46 SkPoint b{200, 400};
47 SkPoint c{390, 100};
48
49 SkPoint ab = interpolate(a, b, frame);
50 SkPoint bc = interpolate(b, c, frame);
51
52 draw_line(canvas, a, b, paint);
53 draw_line(canvas, b, c, paint);
54
55 paint.setStrokeWidth(1);
56 draw_line(canvas, ab, bc, paint);
57 paint.setStrokeWidth(5);
58
59 paint.setColor(SkColorSetARGB(255,0,0,255));
60 SkPath quadraticCurve;
61 quadraticCurve.moveTo(a);
62 quadraticCurve.quadTo(b, c);
63 canvas->drawPath(quadraticCurve, paint);
64
65 SkPaint textPaint;
66 SkFont font(nullptr, 32);
67 textPaint.setAntiAlias(true);
68 canvas->drawString("a", a.x(), a.y(), font, textPaint);
69 canvas->drawString("b", b.x()+20, b.y()+20, font, textPaint);
70 canvas->drawString("c", c.x(), c.y(), font, textPaint);
71
72 SkPaint pointPaint;
73 pointPaint.setAntiAlias(true);
74 pointPaint.setStrokeWidth(8);
75 pointPaint.setStrokeCap(SkPaint::kRound_Cap);
76 pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
77 draw_point(canvas, quad(a, b, c, frame), pointPaint);
78 }
79 } // END FIDDLE
80