add:curve

b00-阅读笔记/zrender源码/z.md

@@ -27,6 +27,86 @@ var zrender = {
 
 ## src/core
 
-### src/core/arrayDiff.js
+### arrayDiff.js
 
 > 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.
+
+### 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)