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# zrender
## 概览
```js
// 对外暴露一个对象
var zrender = {
version: '4.0.7',
init: function (dom, opts) {},
dispose: function (zr) {},
getInstance: function (id) {},
registerPainter: function (name, Ctor) {}
// ...... other interface：
};
```
## 内部类
* ZRender
## 几个重要内部对象(类实例)
* Storage（ ）
* Painter（ ）
* Handler（ ）
* Animation
## src/core
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### arrayDiff.js
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> If x and y are strings, where length(x) = n and length(y) = m, the Needleman-Wunsch algorithm finds an optimal alignment in O(nm) time, using O(nm) space. Hirschberg's algorithm is a clever modification of the Needleman-Wunsch Algorithm which still takes O (nm) time, but needs only O(min{n,m}) space and is much faster in practice.
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### bbox.js
* 从顶点数组中计算出最小包围盒
* 从直线计算最小包围盒
* 从三阶贝塞尔曲线(p0, p1, p2, p3)中计算出最小包围盒
* 从二阶贝塞尔曲线(p0, p1, p2)中计算出最小包围盒
* 从圆弧中计算出最小包围盒
### BoundingRect.js
### curve.js
计算二/三次方贝塞尔值
```js
function quadraticAt(p0, p1, p2, t) {
return (1 - t) * (1 - t) * p0 + 2 * (1 - t) * t * p1 + t * t * p2;
}
function cubicAt(p0, p1, p2, p3, t) {
return (1 - t) * (1 - t) * (1 - t) * p0 + 3 * (1 - t) * (1 - t) * t * p1 + 3 * (1 - t) * t * t * p2 + t * t * t * p3;
}
```
计算二/三次方贝塞尔导数值
```js
function quadraticDerivativeAt(p0, p1, p2, t) {
return 2 * ((1 - t) * (p1 - p0) + t * (p2 - p1));
}
function cubicDerivativeAt(p0, p1, p2, p3, t) {
return 3 * ((1 - t) * (1 - t) * (p1 - p0) + 2 * (1 - t) * t * (p2 - p1) + t * t * (p3 - p2));
}
```
计算二/三次方贝塞尔方程根
[盛金公式 ](https://blog.csdn.net/liutaojia/article/details/83005533 )
计算二/三次贝塞尔方程极限值
```js
//令导数值为零，求出对应的 t 值
function quadraticExtremum(p0, p1, p2) {
var divider = p0 + p2 - 2 * p1;
if (divider === 0) {
// p1 is center of p0 and p2
return 0.5;
}
else {
return (p0 - p1) / divider;
}
}
```
细分二/三次贝塞尔曲线（过细分点切线与始末切线的交点）
```js
function quadraticSubdivide(p0, p1, p2, t, out) {
var p01 = (p1 - p0) * t + p0;
var p12 = (p2 - p1) * t + p1;
var p012 = (p12 - p01) * t + p01;
// seg0
out[0] = p0;
out[1] = p01;
out[2] = p012;
// seg1
out[3] = p012;
out[4] = p12;
out[5] = p2;
}
```
投射点到二/三次贝塞尔曲线上，返回投射距离（一个或者多个，这里只返回其中距离最短的一个）。
[根据已知点找曲线上离它最近的点 ](https://pomax.github.io/bezierinfo/#projections )
