utils增加计算折线的平行线

src/jlgraphic/utils/GraphicUtils.ts

@@ -695,33 +695,43 @@ export function splitLineEvenly(
     });
 }
 
-/** 计算直线的平行线 */
-export function getParallelOfLine(
+export function getParallelOfPolyline(
   points: IPointData[],
-  direction: 'L' | 'R',
-  offset: number
-) {
-  if (points.length !== 2) throw Error('直线点的个数需为2');
-  const normalVecs = points.map((p, i) => {
-    let point;
-    if (points[i + 1]) {
-      point = new Vector2([
-        points[i + 1].x - p.x,
-        points[i + 1].y - p.y,
-      ]).normalize();
+  offset: number,
+  side: 'L' | 'R'
+): IPointData[] {
+  const { PI, cos, acos } = Math;
+  const angleBase = side === 'L' ? -PI / 2 : PI / 2;
+  return points.map((p, i) => {
+    let baseUnitVec: Vector2; //上一段的基准单位向量
+    let angle: number; //偏转角度
+    let len: number; //结合偏转角度的实际偏移量
+    if (!points[i - 1] || !points[i + 1]) {
+      angle = angleBase;
+      len = offset;
+      baseUnitVec = points[i - 1]
+        ? new Vector2([
+            p.x - points[i - 1].x,
+            p.y - points[i - 1].y,
+          ]).normalize()
+        : new Vector2([
+            points[i + 1].x - p.x,
+            points[i + 1].y - p.y,
+          ]).normalize();
     } else {
-      point = new Vector2([
-        p.x - points[i - 1].x,
-        p.y - points[i - 1].y,
-      ]).normalize();
+      const vp = new Vector2([p.x - points[i - 1].x, p.y - points[i - 1].y]);
+      const vn = new Vector2([points[i + 1].x - p.x, points[i + 1].y - p.y]);
+      const cosTheta = Vector2.dot(vn, vp) / (vp.length() * vn.length());
+      const direction = vp.x * vn.y - vp.y * vn.x > 0; //det(vp|vn)>0?
+      const theta = direction ? acos(cosTheta) : -acos(cosTheta);
+      angle = angleBase + theta / 2;
+      len = offset / cos(theta / 2);
+      baseUnitVec = Vector2.from(vp).normalize();
     }
-    const rotate = new Matrix().rotate(
-      (direction === 'L' ? Math.PI : -Math.PI) / 2
-    );
-    return rotate.apply(point);
+    return new Matrix()
+      .scale(len, len)
+      .rotate(angle)
+      .translate(p.x, p.y)
+      .apply(baseUnitVec);
   });
-  return points.map((p, i) => ({
-    x: p.x + offset * normalVecs[i]?.x,
-    y: p.y + offset * normalVecs[i]?.y,
-  }));
 }