added an explanatory comment

package.json

@@ -53,7 +53,7 @@
     "pwacompat": "2.0.17",
     "react": "18.2.0",
     "react-dom": "18.2.0",
-    "roughjs": "4.6.4",
+    "roughjs": "4.6.5",
     "sass": "1.51.0",
     "socket.io-client": "2.3.1",
     "tunnel-rat": "0.1.2"

src/components/App.tsx

@@ -3750,9 +3750,32 @@ class App extends React.Component<AppProps, AppState> {
       return;
     }
 
+    let { x: sceneX, y: sceneY } = viewportCoordsToSceneCoords(
+      event,
+      this.state,
+    );
+
     const selectedElements = this.scene.getSelectedElements(this.state);
 
     if (selectedElements.length === 1 && isLinearElement(selectedElements[0])) {
+      if (!event[KEYS.CTRL_OR_CMD]) {
+        // If double clicked without any ctrl/cmd modifier on top of a point,
+        // toggle split mode for that point. Else, treat as regular double click.
+        const pointUnderCursorIndex =
+          LinearElementEditor.getPointIndexUnderCursor(
+            selectedElements[0],
+            this.state.zoom,
+            sceneX,
+            sceneY,
+          );
+        if (pointUnderCursorIndex >= 0) {
+          LinearElementEditor.toggleSegmentSplitAtIndex(
+            selectedElements[0],
+            pointUnderCursorIndex,
+          );
+          return;
+        }
+      }
       if (
         event[KEYS.CTRL_OR_CMD] &&
         (!this.state.editingLinearElement ||
@@ -3776,11 +3799,6 @@ class App extends React.Component<AppProps, AppState> {
 
     resetCursor(this.interactiveCanvas);
 
-    let { x: sceneX, y: sceneY } = viewportCoordsToSceneCoords(
-      event,
-      this.state,
-    );
-
     const selectedGroupIds = getSelectedGroupIds(this.state);
 
     if (selectedGroupIds.length > 0) {

src/data/restore.ts

@@ -285,6 +285,9 @@ const restoreElement = (
         points,
         x,
         y,
+        segmentSplitIndices: element.segmentSplitIndices
+          ? [...element.segmentSplitIndices]
+          : [],
       });
     }
 

src/element/bounds.ts

@@ -741,7 +741,7 @@ export const getElementPointsCoords = (
   element: ExcalidrawLinearElement,
   points: readonly (readonly [number, number])[],
 ): [number, number, number, number] => {
-  // This might be computationally heavey
+  // This might be computationally heavy
   const gen = rough.generator();
   const curve =
     element.roundness == null

src/element/linearElementEditor.ts

@@ -547,7 +547,10 @@ export class LinearElementEditor {
     endPointIndex: number,
   ) {
     let segmentMidPoint = centerPoint(startPoint, endPoint);
-    if (element.points.length > 2 && element.roundness) {
+    const splits = element.segmentSplitIndices || [];
+    const treatAsCurve =
+      splits.includes(endPointIndex) || splits.includes(endPointIndex - 1);
+    if (element.points.length > 2 && (element.roundness || treatAsCurve)) {
       const controlPoints = getControlPointsForBezierCurve(
         element,
         element.points[endPointIndex],
@@ -1042,13 +1045,15 @@ export class LinearElementEditor {
     let offsetX = 0;
     let offsetY = 0;
 
-    const isDeletingOriginPoint = pointIndices.includes(0);
+    const indexSet = new Set(pointIndices);
+
+    const isDeletingOriginPoint = indexSet.has(0);
 
     // if deleting first point, make the next to be [0,0] and recalculate
     // positions of the rest with respect to it
     if (isDeletingOriginPoint) {
       const firstNonDeletedPoint = element.points.find((point, idx) => {
-        return !pointIndices.includes(idx);
+        return !indexSet.has(idx);
       });
       if (firstNonDeletedPoint) {
         offsetX = firstNonDeletedPoint[0];
@@ -1057,7 +1062,7 @@ export class LinearElementEditor {
     }
 
     const nextPoints = element.points.reduce((acc: Point[], point, idx) => {
-      if (!pointIndices.includes(idx)) {
+      if (!indexSet.has(idx)) {
         acc.push(
           !acc.length ? [0, 0] : [point[0] - offsetX, point[1] - offsetY],
         );
@@ -1065,7 +1070,22 @@ export class LinearElementEditor {
       return acc;
     }, []);
 
-    LinearElementEditor._updatePoints(element, nextPoints, offsetX, offsetY);
+    const splits: number[] = [];
+    (element.segmentSplitIndices || []).forEach((index) => {
+      if (!indexSet.has(index)) {
+        let shift = 0;
+        for (const pointIndex of pointIndices) {
+          if (index > pointIndex) {
+            shift++;
+          }
+        }
+        splits.push(index - shift);
+      }
+    });
+
+    LinearElementEditor._updatePoints(element, nextPoints, offsetX, offsetY, {
+      segmentSplitIndices: splits.sort((a, b) => a - b),
+    });
   }
 
   static addPoints(
@@ -1204,9 +1224,13 @@ export class LinearElementEditor {
       midpoint,
       ...element.points.slice(segmentMidpoint.index!),
     ];
+    const splits = (element.segmentSplitIndices || []).map((index) =>
+      index >= segmentMidpoint.index! ? index + 1 : index,
+    );
 
     mutateElement(element, {
       points,
+      segmentSplitIndices: splits.sort((a, b) => a - b),
     });
 
     ret.pointerDownState = {
@@ -1226,7 +1250,11 @@ export class LinearElementEditor {
     nextPoints: readonly Point[],
     offsetX: number,
     offsetY: number,
-    otherUpdates?: { startBinding?: PointBinding; endBinding?: PointBinding },
+    otherUpdates?: {
+      startBinding?: PointBinding;
+      endBinding?: PointBinding;
+      segmentSplitIndices?: number[];
+    },
   ) {
     const nextCoords = getElementPointsCoords(element, nextPoints);
     const prevCoords = getElementPointsCoords(element, element.points);
@@ -1472,6 +1500,27 @@ export class LinearElementEditor {
 
     return coords;
   };
+
+  static toggleSegmentSplitAtIndex(
+    element: NonDeleted<ExcalidrawLinearElement>,
+    index: number,
+  ) {
+    let found = false;
+    const splitIndices = (element.segmentSplitIndices || []).filter((idx) => {
+      if (idx === index) {
+        found = true;
+        return false;
+      }
+      return true;
+    });
+    if (!found) {
+      splitIndices.push(index);
+    }
+
+    mutateElement(element, {
+      segmentSplitIndices: splitIndices.sort((a, b) => a - b),
+    });
+  }
 }
 
 const normalizeSelectedPoints = (

src/element/mutateElement.ts

@@ -25,7 +25,7 @@ export const mutateElement = <TElement extends Mutable<ExcalidrawElement>>(
 
   // casting to any because can't use `in` operator
   // (see https://github.com/microsoft/TypeScript/issues/21732)
-  const { points, fileId } = updates as any;
+  const { points, fileId, segmentSplitIndices } = updates as any;
 
   if (typeof points !== "undefined") {
     updates = { ...getSizeFromPoints(points), ...updates };
@@ -86,6 +86,7 @@ export const mutateElement = <TElement extends Mutable<ExcalidrawElement>>(
   if (
     typeof updates.height !== "undefined" ||
     typeof updates.width !== "undefined" ||
+    typeof segmentSplitIndices !== "undefined" ||
     typeof fileId != "undefined" ||
     typeof points !== "undefined"
   ) {

src/element/newElement.ts

@@ -374,6 +374,7 @@ export const newLinearElement = (
     endBinding: null,
     startArrowhead: opts.startArrowhead || null,
     endArrowhead: opts.endArrowhead || null,
+    segmentSplitIndices: [],
   };
 };
 

src/element/types.ts

@@ -195,6 +195,7 @@ export type ExcalidrawLinearElement = _ExcalidrawElementBase &
   Readonly<{
     type: "line" | "arrow";
     points: readonly Point[];
+    segmentSplitIndices: readonly number[] | null;
     lastCommittedPoint: Point | null;
     startBinding: PointBinding | null;
     endBinding: PointBinding | null;

src/renderer/renderScene.ts

@@ -166,6 +166,21 @@ const fillCircle = (
   }
 };
 
+const fillSquare = (
+  context: CanvasRenderingContext2D,
+  cx: number,
+  cy: number,
+  side: number,
+  stroke = true,
+) => {
+  context.beginPath();
+  context.rect(cx - side / 2, cy - side / 2, side, side);
+  context.fill();
+  if (stroke) {
+    context.stroke();
+  }
+};
+
 const strokeGrid = (
   context: CanvasRenderingContext2D,
   gridSize: number,
@@ -224,6 +239,7 @@ const renderSingleLinearPoint = (
   point: Point,
   radius: number,
   isSelected: boolean,
+  renderAsSquare: boolean,
   isPhantomPoint = false,
 ) => {
   context.strokeStyle = "#5e5ad8";
@@ -235,13 +251,29 @@ const renderSingleLinearPoint = (
     context.fillStyle = "rgba(177, 151, 252, 0.7)";
   }
 
-  fillCircle(
+  const effectiveRadius = radius / appState.zoom.value;
+
+  if (renderAsSquare) {
+    fillSquare(
       context,
       point[0],
       point[1],
-    radius / appState.zoom.value,
+      effectiveRadius * 2,
       !isPhantomPoint,
     );
+  } else {
+    fillCircle(context, point[0], point[1], effectiveRadius, !isPhantomPoint);
+  }
+};
+
+const isLinearPointAtIndexSquared = (
+  element: NonDeleted<ExcalidrawLinearElement>,
+  index: number,
+) => {
+  const splitting = element.segmentSplitIndices
+    ? element.segmentSplitIndices.includes(index)
+    : false;
+  return element.roundness ? splitting : !splitting;
 };
 
 const renderLinearPointHandles = (
@@ -265,7 +297,14 @@ const renderLinearPointHandles = (
     const isSelected =
       !!appState.editingLinearElement?.selectedPointsIndices?.includes(idx);
 
-    renderSingleLinearPoint(context, appState, point, radius, isSelected);
+    renderSingleLinearPoint(
+      context,
+      appState,
+      point,
+      radius,
+      isSelected,
+      isLinearPointAtIndexSquared(element, idx),
+    );
   });
 
   //Rendering segment mid points
@@ -293,6 +332,7 @@ const renderLinearPointHandles = (
           segmentMidPoint,
           radius,
           false,
+          false,
         );
         highlightPoint(segmentMidPoint, context, appState);
       } else {
@@ -303,6 +343,7 @@ const renderLinearPointHandles = (
           segmentMidPoint,
           radius,
           false,
+          false,
         );
       }
     } else if (appState.editingLinearElement || points.length === 2) {
@@ -312,6 +353,7 @@ const renderLinearPointHandles = (
         segmentMidPoint,
         POINT_HANDLE_SIZE / 2,
         false,
+        false,
         true,
       );
     }
@@ -324,16 +366,16 @@ const highlightPoint = (
   point: Point,
   context: CanvasRenderingContext2D,
   appState: InteractiveCanvasAppState,
+  renderAsSquare = false,
 ) => {
   context.fillStyle = "rgba(105, 101, 219, 0.4)";
+  const radius = LinearElementEditor.POINT_HANDLE_SIZE / appState.zoom.value;
 
-  fillCircle(
-    context,
-    point[0],
-    point[1],
-    LinearElementEditor.POINT_HANDLE_SIZE / appState.zoom.value,
-    false,
-  );
+  if (renderAsSquare) {
+    fillSquare(context, point[0], point[1], radius * 2, false);
+  } else {
+    fillCircle(context, point[0], point[1], radius, false);
+  }
 };
 const renderLinearElementPointHighlight = (
   context: CanvasRenderingContext2D,
@@ -355,10 +397,15 @@ const renderLinearElementPointHighlight = (
     element,
     hoverPointIndex,
   );
+
   context.save();
   context.translate(appState.scrollX, appState.scrollY);
-
-  highlightPoint(point, context, appState);
+  highlightPoint(
+    point,
+    context,
+    appState,
+    isLinearPointAtIndexSquared(element, hoverPointIndex),
+  );
   context.restore();
 };
 

src/scene/Shape.ts

@@ -14,6 +14,7 @@ import { generateFreeDrawShape } from "../renderer/renderElement";
 import { isTransparent, assertNever } from "../utils";
 import { simplify } from "points-on-curve";
 import { ROUGHNESS } from "../constants";
+import { Point } from "../types";
 
 const getDashArrayDashed = (strokeWidth: number) => [8, 8 + strokeWidth];
 
@@ -228,18 +229,44 @@ export const _generateElementShape = (
 
       // points array can be empty in the beginning, so it is important to add
       // initial position to it
-      const points = element.points.length ? element.points : [[0, 0]];
+      const points = element.points.length
+        ? element.points
+        : ([[0, 0]] as Point[]);
 
       // curve is always the first element
       // this simplifies finding the curve for an element
+      const splits = element.segmentSplitIndices || [];
       if (!element.roundness) {
+        if (splits.length === 0) {
           if (options.fill) {
             shape = [generator.polygon(points as [number, number][], options)];
           } else {
-          shape = [generator.linearPath(points as [number, number][], options)];
+            shape = [
+              generator.linearPath(points as [number, number][], options),
+            ];
           }
         } else {
-        shape = [generator.curve(points as [number, number][], options)];
+          const splitInverse: number[] = [];
+          const splitSet = new Set(splits);
+          for (let i = 0; i < points.length; i++) {
+            if (!splitSet.has(i)) {
+              splitInverse.push(i);
+            }
+          }
+          shape = [
+            generator.curve(
+              computeMultipleCurvesFromSplits(points, splitInverse),
+              options,
+            ),
+          ];
+        }
+      } else {
+        shape = [
+          generator.curve(
+            computeMultipleCurvesFromSplits(points, splits),
+            options,
+          ),
+        ];
       }
 
       // add lines only in arrow
@@ -376,3 +403,22 @@ export const _generateElementShape = (
     }
   }
 };
+
+const computeMultipleCurvesFromSplits = (
+  points: readonly Point[],
+  splits: readonly number[],
+): [number, number][][] => {
+  const pointList: Point[][] = [];
+  let currentIndex = 0;
+  for (const index of splits) {
+    const slice = points.slice(currentIndex, index + 1);
+    if (slice.length) {
+      pointList.push([...slice]);
+    }
+    currentIndex = index;
+  }
+  if (currentIndex < points.length - 1) {
+    pointList.push(points.slice(currentIndex));
+  }
+  return pointList as [number, number][][];
+};

yarn.lock

@@ -6459,10 +6459,10 @@ rollup@^3.25.2:
   optionalDependencies:
     fsevents "~2.3.2"
 
-roughjs@4.6.4:
-  version "4.6.4"
-  resolved "https://registry.yarnpkg.com/roughjs/-/roughjs-4.6.4.tgz#b6f39b44645854a6e0a4a28b078368701eb7f939"
-  integrity sha512-s6EZ0BntezkFYMf/9mGn7M8XGIoaav9QQBCnJROWB3brUWQ683Q2LbRD/hq0Z3bAJ/9NVpU/5LpiTWvQMyLDhw==
+roughjs@4.6.5:
+  version "4.6.5"
+  resolved "https://registry.yarnpkg.com/roughjs/-/roughjs-4.6.5.tgz#1db965cf1a043cb7f05181dd7d119f7960fba8d8"
+  integrity sha512-4Q6XBbZWlp8yj1uipq2bQ1CPlxMhW/ukufwkuhh+2L79utk+O5kMSbfVh4UNBMtKJ3PxHQ9Ou3ncNt1iQcphJA==
   dependencies:
     hachure-fill "^0.5.2"
     path-data-parser "^0.1.0"