77 lines
2.5 KiB
C++
77 lines
2.5 KiB
C++
|
// Copyright 2020 Google LLC.
|
||
|
|
// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
|
||
|
|
#include "tools/fiddle/examples.h"
|
||
|
|
REG_FIDDLE(SkPath_cubicTo_example_parametric, 512, 512, false, 0) {
|
||
|
|
/*
|
||
|
|
If the starting point is (x0, y0), then this curve is defined as the
|
||
|
|
paramentric curve as `t` goes from 0 to 1:
|
||
|
|
s := 1 - t
|
||
|
|
x := (s * s * s * x0) +
|
||
|
|
(3 * s * s * t * x1) +
|
||
|
|
(3 * s * t * t * x2) +
|
||
|
|
(t * t * t * x3)
|
||
|
|
y := (s * s * s * y0) +
|
||
|
|
(3 * s * s * t * y1) +
|
||
|
|
(3 * s * t * t * y2) +
|
||
|
|
(t * t * t * y3)
|
||
|
|
|
||
|
|
*/
|
||
|
|
|
||
|
|
SkPoint cubic(SkPoint p0, SkPoint p1, SkPoint p2, SkPoint p3, float t) {
|
||
|
|
float s = 1 - t;
|
||
|
|
return {(s * s * s * p0.x()) + (3 * s * s * t * p1.x()) + (3 * s * t * t * p2.x()) +
|
||
|
|
(t * t * t * p3.x()),
|
||
|
|
(s * s * s * p0.y()) + (3 * s * s * t * p1.y()) + (3 * s * t * t * p2.y()) +
|
||
|
|
(t * t * t * p3.y())};
|
||
|
|
}
|
||
|
|
|
||
|
|
void draw(SkCanvas* canvas) {
|
||
|
|
canvas->clear(SkColorSetARGB(255, 255, 255, 255));
|
||
|
|
SkFont font(nullptr, 32);
|
||
|
|
|
||
|
|
SkPaint paint;
|
||
|
|
paint.setAntiAlias(true);
|
||
|
|
paint.setStyle(SkPaint::kStroke_Style);
|
||
|
|
paint.setStrokeWidth(5);
|
||
|
|
|
||
|
|
SkPoint a{136, 64};
|
||
|
|
SkPoint b{448, 448};
|
||
|
|
SkPoint c{64, 448};
|
||
|
|
SkPoint d{376, 64};
|
||
|
|
|
||
|
|
SkPath threeSegments;
|
||
|
|
threeSegments.moveTo(a);
|
||
|
|
threeSegments.lineTo(b);
|
||
|
|
threeSegments.lineTo(c);
|
||
|
|
threeSegments.lineTo(d);
|
||
|
|
|
||
|
|
canvas->drawPath(threeSegments, paint);
|
||
|
|
|
||
|
|
paint.setColor(SkColorSetARGB(255, 0, 0, 255));
|
||
|
|
SkPath cubicCurve;
|
||
|
|
cubicCurve.moveTo(a);
|
||
|
|
cubicCurve.cubicTo(b, c, d);
|
||
|
|
canvas->drawPath(cubicCurve, paint);
|
||
|
|
|
||
|
|
SkPaint textPaint;
|
||
|
|
textPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
|
||
|
|
textPaint.setAntiAlias(true);
|
||
|
|
canvas->drawString("a", a.x(), a.y(), font, textPaint);
|
||
|
|
canvas->drawString("b", b.x(), b.y(), font, textPaint);
|
||
|
|
canvas->drawString("c", c.x() - 20, c.y(), font, textPaint);
|
||
|
|
canvas->drawString("d", d.x(), d.y(), font, textPaint);
|
||
|
|
|
||
|
|
SkPaint pointPaint;
|
||
|
|
pointPaint.setAntiAlias(true);
|
||
|
|
pointPaint.setStrokeWidth(8);
|
||
|
|
pointPaint.setStrokeCap(SkPaint::kRound_Cap);
|
||
|
|
pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
|
||
|
|
const int N = 16;
|
||
|
|
for (int i = 0; i <= N; ++i) {
|
||
|
|
SkPoint p = cubic(a, b, c, d, (float)i / N);
|
||
|
|
canvas->drawPoint(p.x(), p.y(), pointPaint);
|
||
|
|
}
|
||
|
|
pointPaint.setColor(SkColorSetARGB(255, 255, 0, 0));
|
||
|
|
}
|
||
|
|
} // END FIDDLE
|