fix(line-snap): prefer bindable targets over external snaps

packages/element/src/linearElementEditor.ts

@@ -52,6 +52,7 @@ import {
   calculateFixedPointForNonElbowArrowBinding,
   getBindingStrategyForDraggingBindingElementEndpoints,
   isBindingEnabled,
+  maxBindingDistance_simple,
   snapToMid,
   updateBoundPoint,
 } from "./binding";
@@ -60,6 +61,7 @@ import {
   getElementPointsCoords,
   getMinMaxXYFromCurvePathOps,
 } from "./bounds";
+import { getHoveredElementForBinding } from "./collision";
 
 import { headingIsHorizontal, vectorToHeading } from "./heading";
 import { mutateElement } from "./mutateElement";
@@ -1890,6 +1892,44 @@ export class LinearElementEditor {
       : app.getEffectiveGridSize();
   }
 
+  private static _shouldSkipExternalSnapForBindableTarget({
+    appState,
+    elements,
+    elementsMap,
+    element,
+    pointIndex,
+    scenePoint,
+    selectedPointsIndices,
+  }: {
+    appState: AppState;
+    elements: readonly Ordered<NonDeletedExcalidrawElement>[];
+    elementsMap: NonDeletedSceneElementsMap;
+    element: NonDeleted<ExcalidrawLinearElement>;
+    pointIndex: number;
+    scenePoint: GlobalPoint;
+    selectedPointsIndices?: readonly number[];
+  }) {
+    if (
+      isElbowArrow(element) ||
+      !isBindingElement(element) ||
+      !isBindingEnabled(appState) ||
+      selectedPointsIndices?.length !== 1
+    ) {
+      return false;
+    }
+
+    if (pointIndex !== 0 && pointIndex !== element.points.length - 1) {
+      return false;
+    }
+
+    return !!getHoveredElementForBinding(
+      scenePoint,
+      elements,
+      elementsMap,
+      maxBindingDistance_simple(appState.zoom),
+    );
+  }
+
   private static _getSnappedPointForLinearElement({
     app,
     event,
@@ -1952,6 +1992,16 @@ export class LinearElementEditor {
       const effectiveGridY = referencePointCoords[1] + dyFromReference;
 
       let snapLines: SnapLine[] = [];
+      const shouldSkipExternalSnap =
+        LinearElementEditor._shouldSkipExternalSnapForBindableTarget({
+          appState: app.state,
+          elements,
+          elementsMap,
+          element,
+          pointIndex,
+          scenePoint: pointFrom<GlobalPoint>(effectiveGridX, effectiveGridY),
+          selectedPointsIndices,
+        });
 
       if (!isElbowArrow(element)) {
         const { snapOffset, snapLines: nextSnapLines } = snapLinearElementPoint(
@@ -1962,6 +2012,7 @@ export class LinearElementEditor {
           event,
           elementsMap,
           {
+            includeExternalPoints: !shouldSkipExternalSnap,
             includeSelfPoints: true,
             selectedPointsIndices,
           },
@@ -2010,6 +2061,16 @@ export class LinearElementEditor {
 
     const originalPointerX = scenePointerX - pointerOffset.x;
     const originalPointerY = scenePointerY - pointerOffset.y;
+    const shouldSkipExternalSnap =
+      LinearElementEditor._shouldSkipExternalSnapForBindableTarget({
+        appState: app.state,
+        elements,
+        elementsMap,
+        element,
+        pointIndex,
+        scenePoint: pointFrom<GlobalPoint>(originalPointerX, originalPointerY),
+        selectedPointsIndices,
+      });
 
     const { snapOffset, snapLines } = snapLinearElementPoint(
       elements,
@@ -2019,6 +2080,7 @@ export class LinearElementEditor {
       event,
       elementsMap,
       {
+        includeExternalPoints: !shouldSkipExternalSnap,
         includeSelfPoints: true,
         selectedPointsIndices,
       },

packages/element/src/snapping.ts

@@ -804,6 +804,7 @@ export const snapLinearElementPoint = (
   event: KeyboardModifiersObject,
   elementsMap: ElementsMap,
   options: {
+    includeExternalPoints?: boolean;
     includeSelfPoints?: boolean;
     selectedPointsIndices?: readonly number[];
   } = {},
@@ -827,6 +828,7 @@ export const snapLinearElementPoint = (
   const nearestSnapsX: Snaps = [];
   const nearestSnapsY: Snaps = [];
 
+  if (options.includeExternalPoints !== false) {
     collectNearestAxisSnapCandidates(
       getExternalAxisSnapTargets(
         elements,
@@ -839,6 +841,7 @@ export const snapLinearElementPoint = (
       nearestSnapsY,
       minOffset,
     );
+  }
 
   if (options.includeSelfPoints) {
     collectNearestAxisSnapCandidates(

packages/element/tests/linearElementEditor.test.tsx

@@ -313,6 +313,36 @@ describe("Test Linear Elements", () => {
     expect(endpoint).toEqual(pointFrom<GlobalPoint>(100, 100));
   });
 
+  it("prefers binding over external snaps when creating an arrow endpoint", () => {
+    const rect = API.createElement({
+      type: "rectangle",
+      x: 100,
+      y: 100,
+      width: 40,
+      height: 40,
+    });
+    API.setElements([rect]);
+    API.setAppState({ objectsSnapModeEnabled: true });
+
+    UI.clickTool("arrow");
+
+    const startPoint = pointFrom<GlobalPoint>(20, 20);
+    const pointerNearBindable = pointFrom<GlobalPoint>(96, 118);
+
+    dragMove(startPoint, pointerNearBindable);
+
+    expect(h.state.suggestedBinding?.element.id).toBe(rect.id);
+    expect(h.state.snapLines).toEqual([]);
+
+    dragEnd(pointerNearBindable);
+
+    const arrow = h.elements.find(
+      (element): element is ExcalidrawLinearElement => element.type === "arrow",
+    );
+
+    expect(arrow?.endBinding?.elementId).toBe(rect.id);
+  });
+
   it("should enter line editor via enter (line)", () => {
     createTwoPointerLinearElement("line");
     expect(h.state.selectedLinearElement?.isEditing).toBe(false);
@@ -489,6 +519,44 @@ describe("Test Linear Elements", () => {
       );
     });
 
+    it("prefers binding over external snaps when dragging an existing arrow endpoint", () => {
+      const rect = API.createElement({
+        type: "rectangle",
+        x: 100,
+        y: 100,
+        width: 40,
+        height: 40,
+      });
+      const arrow = API.createElement({
+        type: "arrow",
+        x: 20,
+        y: 20,
+        width: 40,
+        height: 0,
+        points: [pointFrom<LocalPoint>(0, 0), pointFrom<LocalPoint>(40, 0)],
+      });
+
+      API.setElements([rect, arrow]);
+      API.setAppState({ objectsSnapModeEnabled: true });
+      enterLineEditingMode(arrow);
+
+      const endPoint = LinearElementEditor.getPointGlobalCoordinates(
+        arrow,
+        arrow.points[arrow.points.length - 1],
+        h.app.scene.getNonDeletedElementsMap(),
+      );
+      const pointerNearBindable = pointFrom<GlobalPoint>(96, 118);
+
+      dragMove(endPoint, pointerNearBindable);
+
+      expect(h.state.suggestedBinding?.element.id).toBe(rect.id);
+      expect(h.state.snapLines).toEqual([]);
+
+      dragEnd(pointerNearBindable);
+
+      expect(API.getElement(arrow).endBinding?.elementId).toBe(rect.id);
+    });
+
     it("should update the midpoints when element roundness changed", async () => {
       createThreePointerLinearElement("line");