08-27-周三_17-09-29

node_modules/dagre-d3-renderer/lib/intersect/intersect-line.js

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+/*
+ * Returns the point at which two lines, p and q, intersect or returns
+ * undefined if they do not intersect.
+ */
+function intersectLine (p1, p2, q1, q2) {
+  // Algorithm from J. Avro, (ed.) Graphics Gems, No 2, Morgan Kaufmann, 1994,
+  // p7 and p473.
+
+  // Compute a1, b1, c1, where line joining points 1 and 2 is F(x,y) = a1 x +
+  // b1 y + c1 = 0.
+  const a1 = p2.y - p1.y
+  const b1 = p1.x - p2.x
+  const c1 = (p2.x * p1.y) - (p1.x * p2.y)
+
+  // Compute r3 and r4.
+  const r3 = ((a1 * q1.x) + (b1 * q1.y) + c1)
+  const r4 = ((a1 * q2.x) + (b1 * q2.y) + c1)
+
+  // Check signs of r3 and r4. If both point 3 and point 4 lie on
+  // same side of line 1, the line segments do not intersect.
+  if ((r3 !== 0) && (r4 !== 0) && sameSign(r3, r4)) {
+    return /* DONT_INTERSECT */
+  }
+
+  // Compute a2, b2, c2 where line joining points 3 and 4 is G(x,y) = a2 x + b2 y + c2 = 0
+  const a2 = q2.y - q1.y
+  const b2 = q1.x - q2.x
+  const c2 = (q2.x * q1.y) - (q1.x * q2.y)
+
+  // Compute r1 and r2
+  const r1 = (a2 * p1.x) + (b2 * p1.y) + c2
+  const r2 = (a2 * p2.x) + (b2 * p2.y) + c2
+
+  // Check signs of r1 and r2. If both point 1 and point 2 lie
+  // on same side of second line segment, the line segments do
+  // not intersect.
+  if ((r1 !== 0) && (r2 !== 0) && (sameSign(r1, r2))) {
+    return /* DONT_INTERSECT */
+  }
+
+  // Line segments intersect: compute intersection point.
+  const denom = (a1 * b2) - (a2 * b1)
+  if (denom === 0) {
+    return /* COLLINEAR */
+  }
+
+  const offset = Math.abs(denom / 2)
+
+  // The denom/2 is to get rounding instead of truncating. It
+  // is added or subtracted to the numerator, depending upon the
+  // sign of the numerator.
+  let num = (b1 * c2) - (b2 * c1)
+  const x = (num < 0) ? ((num - offset) / denom) : ((num + offset) / denom)
+
+  num = (a2 * c1) - (a1 * c2)
+  const y = (num < 0) ? ((num - offset) / denom) : ((num + offset) / denom)
+
+  return { x, y }
+}
+
+function sameSign (r1, r2) {
+  return r1 * r2 > 0
+}
+
+export default intersectLine