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 
cubic(SkPoint p0,SkPoint p1,SkPoint p2,SkPoint p3,float t)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 
interpolate(SkPoint a,SkPoint b,float t)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 
draw(SkCanvas * canvas)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
101