Angle based line checking

src/shapes.js

@@ -73,12 +73,48 @@ function boundingCoords(points) {
   }
 }
 
-const LINE_Q = 10
+function vectorLength([x, y]) {
+  return Math.hypot(x, y)
+}
+
+function diffVector([x0, y0], [x1, y1]) {
+  return [x0 - x1, y0 - y1]
+}
+
+function angleBetweenVectors(p1, p2) {
+  const [[x0, y0], [x1, y1]] = [p1, p2]
+  return Math.acos((x0 * x1 + y0 * y1) / (vectorLength(p1) * vectorLength(p2)))
+}
+
+const LINE_ANGLE_THRESHOLD = Math.PI / 4
+const VECTOR_LEN_THRESHOLD = 400
 
 function couldBeLine(points) {
-  const { maxX, minX, maxY, minY } = boundingCoords(points)
-  const [dx, dy] = [maxX - minX, maxY - minY].map((x) => x + 0.00001)
-  return dy / dx > LINE_Q || dx / dy > LINE_Q
+  if (points.length < 2) return false
+  const pivot = points[0]
+  let cumulativeThreshold = 0
+  for (let i = 2; i < points.length; i++) {
+    const p1 = points[i - 1]
+    const p2 = points[i]
+    const d1 = diffVector(pivot, p1)
+    const d2 = diffVector(p1, p2)
+
+    const d2Len = vectorLength(d2)
+
+    if (
+      cumulativeThreshold < VECTOR_LEN_THRESHOLD &&
+      d2Len < VECTOR_LEN_THRESHOLD
+    ) {
+      cumulativeThreshold += d2Len
+      continue
+    }
+
+    const angle = angleBetweenVectors(d1, d2)
+    if (Math.abs(angle) > LINE_ANGLE_THRESHOLD) {
+      return false
+    }
+  }
+  return true
 }
 
 const MATRIX_SIZE = 3
@@ -186,7 +222,7 @@ function recognizeLine(points) {
   if (!(points && points.length)) return {}
   const accum = Array(numAngleCells)
   const houghConfig = {
-    rhoStep: points.length > 50 ? 50 : 5,
+    rhoStep: points.length > 30 ? 50 : 5,
   }
   points.forEach((x) => constructHoughAccumulator(houghConfig, accum, ...x))
   const angle = findMaxInHough(accum, points.length - 1)