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94 lines
2.1 KiB
Plaintext
94 lines
2.1 KiB
Plaintext
/**
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* @file 三次贝塞尔转二次贝塞尔
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* @author mengke01(kekee000@gmail.com)
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*
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* references:
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* https://github.com/search?utf8=%E2%9C%93&q=svg2ttf
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* http://www.caffeineowl.com/graphics/2d/vectorial/cubic2quad01.html
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*
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*/
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function toQuad(p1, c1, c2, p2) {
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// Quad control point is (3*c2 - p2 + 3*c1 - p1)/4
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const x = (3 * c2.x - p2.x + 3 * c1.x - p1.x) / 4;
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const y = (3 * c2.y - p2.y + 3 * c1.y - p1.y) / 4;
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return [
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p1,
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{x, y},
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p2
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];
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}
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/**
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* 三次贝塞尔转二次贝塞尔
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*
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* @param {Object} p1 开始点
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* @param {Object} c1 控制点1
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* @param {Object} c2 控制点2
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* @param {Object} p2 结束点
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* @return {Array} 二次贝塞尔控制点
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*/
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export default function bezierCubic2Q2(p1, c1, c2, p2) {
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// 判断极端情况，控制点和起止点一样
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if (p1.x === c1.x && p1.y === c1.y && c2.x === p2.x && c2.y === p2.y) {
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return [
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[
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p1,
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{
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x: (p1.x + p2.x) / 2,
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y: (p1.y + p2.y) / 2
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},
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p2
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]
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];
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}
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const mx = p2.x - 3 * c2.x + 3 * c1.x - p1.x;
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const my = p2.y - 3 * c2.y + 3 * c1.y - p1.y;
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// control points near
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if (mx * mx + my * my <= 4) {
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return [
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toQuad(p1, c1, c2, p2)
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];
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}
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// Split to 2 qubic beziers by midpoints
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// (p2 + 3*c2 + 3*c1 + p1)/8
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const mp = {
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x: (p2.x + 3 * c2.x + 3 * c1.x + p1.x) / 8,
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y: (p2.y + 3 * c2.y + 3 * c1.y + p1.y) / 8
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};
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return [
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toQuad(
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p1,
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{
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x: (p1.x + c1.x) / 2,
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y: (p1.y + c1.y) / 2
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},
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{
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x: (p1.x + 2 * c1.x + c2.x) / 4,
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y: (p1.y + 2 * c1.y + c2.y) / 4
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},
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mp
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),
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toQuad(
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mp,
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{
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x: (p2.x + c1.x + 2 * c2.x) / 4,
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y: (p2.y + c1.y + 2 * c2.y) / 4
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},
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{
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x: (p2.x + c2.x) / 2,
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y: (p2.y + c2.y) / 2
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},
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p2
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)
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];
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}
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