#945 Rendering of labels and new label positioning algorithm

src/utils.js

@@ -73,8 +73,56 @@ export const interpolateToCurve = (interpolate, defaultCurve) => {
   return d3[curveName] || defaultCurve;
 };
 
+const distance = (p1, p2) =>
+  p1 && p2 ? Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2)) : 0;
+
+const traverseEdge = points => {
+  let prevPoint;
+  let totalDistance = 0;
+
+  points.forEach(point => {
+    totalDistance += distance(point, prevPoint);
+    prevPoint = point;
+  });
+
+  // Traverse half of total distance along points
+  const distanceToLabel = totalDistance / 2;
+
+  let remainingDistance = distanceToLabel;
+  let center;
+  prevPoint = undefined;
+  points.forEach(point => {
+    if (prevPoint && !center) {
+      const vectorDistance = distance(point, prevPoint);
+      if (vectorDistance < remainingDistance) {
+        remainingDistance -= vectorDistance;
+      } else {
+        // The point is remainingDistance from prevPoint in the vector between prevPoint and point
+        // Calculate the coordinates
+        const distanceRatio = remainingDistance / vectorDistance;
+        if (distanceRatio <= 0) center = prevPoint;
+        if (distanceRatio >= 1) center = { x: point.x, y: point.y };
+        if (distanceRatio > 0 && distanceRatio < 1) {
+          center = {
+            x: (1 - distanceRatio) * prevPoint.x + distanceRatio * point.x,
+            y: (1 - distanceRatio) * prevPoint.y + distanceRatio * point.y
+          };
+        }
+      }
+    }
+    prevPoint = point;
+  });
+  return center;
+};
+
+const calcLabelPosition = points => {
+  const p = traverseEdge(points);
+  return p;
+};
+
 export default {
   detectType,
   isSubstringInArray,
-  interpolateToCurve
+  interpolateToCurve,
+  calcLabelPosition
 };