skia2/docs/examples/SkPath_cubicTo_example_parametric.cpp
Hal Canary 6c8422c671 add more docs/examples from named fiddles.
ignore offscreen, srgb, and animated fiddles for now.

Change-Id: I923131b684865698e6cda138b004930e11f504d5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/263713
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
2020-01-14 19:22:26 +00:00

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