Intuitive erasing

Closes !49 (closed).

src/erasure.js

-function sqr(x) {
-  return x ** 2
+function getDistance([x0, y0], [x1, y1]) {
+  return Math.hypot(x1 - x0, y1 - y0)
 }
 
-function hypotenuseSquared(a, b) {
-  return sqr(a) + sqr(b)
+function clamp(x, min, max) {
+  return Math.max(min, Math.min(max, x))
 }
 
-function distanceSquared([x0, y0], [x1, y1]) {
-  return hypotenuseSquared(x0 - x1, y0 - y1)
-}
-
-function distance(point0, point1) {
-  return Math.sqrt(distanceSquared(point0, point1))
-}
-
-function cap01(x) {
-  return Math.max(0, Math.min(1, x))
-}
-
-function distToSegmentSquared(lineStart, lineEnd, point) {
-  const l2 = distanceSquared(lineStart, lineEnd)
-  if (l2 === 0) return distanceSquared(point, lineStart)
+function distToSegment(lineStart, lineEnd, point) {
+  const l = getDistance(lineStart, lineEnd)
+  if (l === 0) return getDistance(point, lineStart)
   let t =
     ((point[0] - lineStart[0]) * (lineEnd[0] - lineStart[0]) +
       (point[1] - lineStart[1]) * (lineEnd[1] - lineStart[1])) /
-    l2
-  t = cap01(t)
-  return distanceSquared(point, [
+    l ** 2
+  t = clamp(t, 0, 1)
+  return getDistance(point, [
     lineStart[0] + t * (lineEnd[0] - lineStart[0]),
     lineStart[1] + t * (lineEnd[1] - lineStart[1]),
   ])
@@ -47,30 +35,30 @@ function project([x1, y1], [x2, y2], [x3, y3]) {
 function erasureInterval(lineStart, lineEnd, erasureCenter, erasureRadius) {
   if (!(lineStart && lineEnd && erasureCenter)) return
 
-  const distToSegment2 = distToSegmentSquared(lineStart, lineEnd, erasureCenter)
-  if (erasureRadius ** 2 < distToSegment2) return
+  const dist = distToSegment(lineStart, lineEnd, erasureCenter)
+  if (erasureRadius < dist) return
 
-  const lineLength = distance(lineStart, lineEnd)
+  const lineLength = getDistance(lineStart, lineEnd)
   if (lineLength === 0) {
-    return distToSegment2 <= erasureRadius ** 2 ? [0, 1] : [0, 0]
+    return dist <= erasureRadius ? [0, 1] : [0, 0]
   }
 
   const projT = project(lineStart, lineEnd, erasureCenter)
   const projectionPoint = interpolate(lineStart, lineEnd, projT)
 
-  const d2 = distance(erasureCenter, projectionPoint)
-  const halfLength = Math.sqrt(Math.abs(sqr(erasureRadius) - sqr(d2)))
+  const d2 = getDistance(erasureCenter, projectionPoint)
+  const halfLength = Math.sqrt(Math.abs(erasureRadius ** 2 - d2 ** 2))
   if (halfLength === 0) return undefined
 
-  let touchFromStartDist = distance(lineStart, projectionPoint)
+  let touchFromStartDist = getDistance(lineStart, projectionPoint)
   if (projT < 0) touchFromStartDist = -touchFromStartDist
 
   const touchBeginFromStarDist = touchFromStartDist - halfLength
   const touchEndFromStarDist = touchFromStartDist + halfLength
 
   return [
-    cap01(touchBeginFromStarDist / lineLength),
-    cap01(touchEndFromStarDist / lineLength),
+    clamp(touchBeginFromStarDist / lineLength, 0, 1),
+    clamp(touchEndFromStarDist / lineLength, 0, 1),
   ]
 }