66 lines
2.0 KiB
C++
66 lines
2.0 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_quadTo_example_parametric, 512, 512, false, 0) {
|
|
SkPoint quad(SkPoint p0, SkPoint p1, SkPoint p2, float t) {
|
|
float s = 1 - t;
|
|
return {(s * s * p0.x()) + (2 * s * t * p1.x()) + (t * t * p2.x()),
|
|
(s * s * p0.y()) + (2 * s * t * p1.y()) + (t * t * p2.y())};
|
|
}
|
|
|
|
/*
|
|
|
|
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 * x0) + (2 * s * t * x1) + (t * t * x2)
|
|
y := (s * s * y0) + (2 * s * t * y1) + (t * t * y2)
|
|
|
|
*/
|
|
|
|
void draw(SkCanvas* canvas) {
|
|
canvas->clear(SkColorSetARGB(255, 255, 255, 255));
|
|
|
|
SkPaint paint;
|
|
paint.setAntiAlias(true);
|
|
paint.setStyle(SkPaint::kStroke_Style);
|
|
paint.setStrokeWidth(5);
|
|
|
|
SkPoint a{100, 100};
|
|
SkPoint b{200, 400};
|
|
SkPoint c{300, 100};
|
|
|
|
SkPath twoSegments;
|
|
twoSegments.moveTo(a);
|
|
twoSegments.lineTo(b);
|
|
twoSegments.lineTo(c);
|
|
|
|
canvas->drawPath(twoSegments, paint);
|
|
|
|
paint.setColor(SkColorSetARGB(255, 0, 0, 255));
|
|
SkPath quadraticCurve;
|
|
quadraticCurve.moveTo(a);
|
|
quadraticCurve.quadTo(b, c);
|
|
canvas->drawPath(quadraticCurve, paint);
|
|
|
|
SkFont font(nullptr, 32);
|
|
SkPaint textPaint;
|
|
textPaint.setAntiAlias(true);
|
|
canvas->drawString("a", a.x(), a.y(), font, textPaint);
|
|
canvas->drawString("b", b.x() + 20, b.y() + 20, font, textPaint);
|
|
canvas->drawString("c", c.x(), c.y(), font, textPaint);
|
|
|
|
SkPaint pointPaint;
|
|
pointPaint.setAntiAlias(true);
|
|
pointPaint.setStrokeWidth(8);
|
|
pointPaint.setStrokeCap(SkPaint::kRound_Cap);
|
|
pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
|
|
int N = 15;
|
|
for (int i = 0; i <= N; ++i) {
|
|
SkPoint p = quad(a, b, c, (float)i / N);
|
|
canvas->drawPoint(p.x(), p.y(), pointPaint);
|
|
}
|
|
}
|
|
} // END FIDDLE
|