80 lines
2.5 KiB
C++
80 lines
2.5 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_ANIMATED(SkPath_quadTo_example_parametric_animated, 512, 512, false, 0, 4) {
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// SkPath_quadTo_example_parametric_animated
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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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static SkPoint interpolate(SkPoint a, SkPoint b, float t) {
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return {SkScalarInterp(a.x(), b.x(), t),
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SkScalarInterp(a.y(), b.y(), t)};
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}
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static void draw_line(SkCanvas* canvas, SkPoint p0, SkPoint p1, const SkPaint& paint) {
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canvas->drawLine(p0.x(), p0.y(), p1.x(), p1.y(), paint);
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}
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static void draw_point(SkCanvas* canvas, SkPoint p, const SkPaint& paint) {
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canvas->drawPoint(p.x(), p.y(), paint);
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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{10, 100};
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SkPoint b{200, 400};
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SkPoint c{390, 100};
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SkPoint ab = interpolate(a, b, frame);
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SkPoint bc = interpolate(b, c, frame);
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draw_line(canvas, a, b, paint);
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draw_line(canvas, b, c, paint);
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paint.setStrokeWidth(1);
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draw_line(canvas, ab, bc, paint);
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paint.setStrokeWidth(5);
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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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SkPaint textPaint;
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SkFont font(nullptr, 32);
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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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draw_point(canvas, quad(a, b, c, frame), pointPaint);
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}
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} // END FIDDLE
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