101 lines
3.4 KiB
C++
101 lines
3.4 KiB
C++
// 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_cubicTo_example_parametric_animated, 512, 512, false, 0, 3) {
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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 * s * x0) +
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(3 * s * s * t * x1) +
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(3 * s * t * t * x2) +
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(t * t * t * x3)
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y := (s * s * s * y0) +
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(3 * s * s * t * y1) +
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(3 * s * t * t * y2) +
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(t * t * t * y3)
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*/
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SkPoint cubic(SkPoint p0, SkPoint p1, SkPoint p2, SkPoint p3, float t) {
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// a simple mathematical definition of cubic curve.
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// There are faster ways to calculate this.
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float s = 1 - t;
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return {(s * s * s * p0.x()) +
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(3 * s * s * t * p1.x()) +
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(3 * s * t * t * p2.x()) +
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(t * t * t * p3.x()),
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(s * s * s * p0.y()) +
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(3 * s * s * t * p1.y()) +
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(3 * s * t * t * p2.y()) +
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(t * t * t * p3.y())};
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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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void draw(SkCanvas* canvas) {
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canvas->clear(SkColorSetARGB(255,255,255,255));
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SkPoint a{136, 64};
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SkPoint b{448, 448};
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SkPoint c{64, 448};
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SkPoint d{376, 64};
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SkPoint ab = interpolate(a, b, frame);
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SkPoint bc = interpolate(b, c, frame);
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SkPoint cd = interpolate(c, d, frame);
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SkPoint abc = interpolate(ab, bc, frame);
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SkPoint bcd = interpolate(bc, cd, frame);
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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(1);
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canvas->drawLine(ab, bc, paint);
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canvas->drawLine(bc, cd, paint);
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canvas->drawLine(abc, bcd, paint);
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paint.setStrokeWidth(3);
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canvas->drawLine(a, b, paint);
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canvas->drawLine(b, c, paint);
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canvas->drawLine(c, d, paint);
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paint.setStrokeWidth(5);
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paint.setColor(SkColorSetARGB(255, 0, 0, 255));
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SkPath cubicCurve;
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cubicCurve.moveTo(a);
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cubicCurve.cubicTo(b, c, d);
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canvas->drawPath(cubicCurve, paint);
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SkFont font(nullptr, 32);
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SkPaint textPaint;
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textPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
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textPaint.setAntiAlias(true);
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sk_sp<SkFontMgr> mgr(SkFontMgr::RefDefault());
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sk_sp<SkTypeface> face(mgr->matchFamilyStyle("DejaVu Sans Mono", SkFontStyle()));
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canvas->drawString("a", a.x(), a.y(), font, textPaint);
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canvas->drawString("b", b.x(), b.y(), font, textPaint);
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canvas->drawString("c", c.x()-20, c.y(), font, textPaint);
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canvas->drawString("d", d.x(), d.y(), font, textPaint);
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SkString msg = SkStringPrintf("%.4f", frame);
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textPaint.setColor(SkColorSetARGB(255, 204, 204, 204));
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canvas->drawString(msg.c_str(), 4, 36, 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, 255, 0, 0));
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canvas->drawPoint(interpolate(abc, bcd, frame), pointPaint);
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pointPaint.setColor(SkColorSetARGB(255, 0, 255, 0));
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pointPaint.setStrokeWidth(7);
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canvas->drawPoint(cubic(a, b, c, d, frame), pointPaint);
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}
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} // END FIDDLE
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