66 lines
2.0 KiB
C++
66 lines
2.0 KiB
C++
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// Copyright 2020 Google LLC.
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// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
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#include "tools/fiddle/examples.h"
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REG_FIDDLE(SkPath_quadTo_example_parametric, 512, 512, false, 0) {
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SkPoint quad(SkPoint p0, SkPoint p1, SkPoint p2, float t) {
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float s = 1 - t;
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return {(s * s * p0.x()) + (2 * s * t * p1.x()) + (t * t * p2.x()),
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(s * s * p0.y()) + (2 * s * t * p1.y()) + (t * t * p2.y())};
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}
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/*
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If the starting point is (x0, y0), then this curve is defined as the
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paramentric curve as `t` goes from 0 to 1:
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s := 1 - t
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x := (s * s * x0) + (2 * s * t * x1) + (t * t * x2)
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y := (s * s * y0) + (2 * s * t * y1) + (t * t * y2)
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*/
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void draw(SkCanvas* canvas) {
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canvas->clear(SkColorSetARGB(255, 255, 255, 255));
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SkPaint paint;
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paint.setAntiAlias(true);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(5);
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SkPoint a{100, 100};
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SkPoint b{200, 400};
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SkPoint c{300, 100};
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SkPath twoSegments;
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twoSegments.moveTo(a);
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twoSegments.lineTo(b);
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twoSegments.lineTo(c);
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canvas->drawPath(twoSegments, paint);
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paint.setColor(SkColorSetARGB(255, 0, 0, 255));
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SkPath quadraticCurve;
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quadraticCurve.moveTo(a);
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quadraticCurve.quadTo(b, c);
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canvas->drawPath(quadraticCurve, paint);
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SkFont font(nullptr, 32);
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SkPaint textPaint;
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textPaint.setAntiAlias(true);
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canvas->drawString("a", a.x(), a.y(), font, textPaint);
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canvas->drawString("b", b.x() + 20, b.y() + 20, font, textPaint);
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canvas->drawString("c", c.x(), c.y(), font, textPaint);
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SkPaint pointPaint;
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pointPaint.setAntiAlias(true);
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pointPaint.setStrokeWidth(8);
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pointPaint.setStrokeCap(SkPaint::kRound_Cap);
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pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
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int N = 15;
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for (int i = 0; i <= N; ++i) {
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SkPoint p = quad(a, b, c, (float)i / N);
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canvas->drawPoint(p.x(), p.y(), pointPaint);
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}
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}
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} // END FIDDLE
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