Allow binding linear elements to other elements (#1899)

* Refactor: simplify linear element type

* Refactor: dedupe scrollbar handling

* First step towards binding - establish relationship and basic test for dragged lines

* Refactor: use zoom from appstate

* Refactor: generalize getElementAtPosition

* Only consider bindable elements in hit test

* Refactor: pull out pieces of hit test for reuse later

* Refactor: pull out diamond from hit test for reuse later

* Refactor: pull out text from hit test for reuse later

* Suggest binding when hovering

* Give shapes in regression test real size

* Give shapes in undo/redo test real size

* Keep bound element highlighted

* Show binding suggestion for multi-point elements

* Move binding to its on module with functions so that I can use it from actions, add support for binding end of multi-point elements

* Use Id instead of ID

* Improve boundary offset for non-squarish elements

* Fix localStorage for binding on linear elements

* Simplify dragging code and fix elements bound twice to the same shape

* Fix binding for rectangles

* Bind both ends at the end of the linear element creation, needed for focus points

* wip

* Refactor: Renames and reshapes for next commit

* Calculate and store focus points and gaps, but dont use them yet

* Focus points for rectangles

* Dont blow up when canceling linear element

* Stop suggesting binding when a non-compatible tool is selected

* Clean up collision code

* Using Geometric Algebra for hit tests

* Correct binding for all shapes

* Constant gap around polygon corners

* Fix rotation handling

* Generalize update and fix hit test for rotated elements

* Handle rotation realtime

* Handle scaling

* Remove vibration when moving bound and binding element together

* Handle simultenous scaling

* Allow binding and unbinding when editing linear elements

* Dont delete binding when the end point wasnt touched

* Bind on enter/escape when editing

* Support multiple suggested bindable elements in preparation for supporting linear elements dragging

* Update binding when moving linear elements

* Update binding when resizing linear elements

* Dont re-render UI on binding hints

* Update both ends when one is moved

* Use distance instead of focus point for binding

* Complicated approach for posterity, ignore this commit

* Revert the complicated approach

* Better focus point strategy, working for all shapes

* Update snapshots

* Dont break binding gap when mirroring shape

* Dont break binding gap when grid mode pushes it inside

* Dont bind draw elements

* Support alt duplication

* Fix alt duplication to

* Support cmd+D duplication

* All copy mechanisms are supported

* Allow binding shapes to arrows, having arrows created first

* Prevent arrows from disappearing for ellipses

* Better binding suggestion highlight for shapes

* Dont suggest second binding for simple elements when editing or moving them

* Dont steal already bound linear elements when moving shapes

* Fix highlighting diamonds and more precisely highlight other shapes

* Highlight linear element edges for binding

* Highlight text binding too

* Handle deletion

* Dont suggest second binding for simple linear elements when creating them

* Dont highlight bound element during creation

* Fix binding for rotated linear elements

* Fix collision check for ellipses

* Dont show suggested bindings for selected pairs

* Bind multi-point linear elements when the tool is switched - important for mobile

* Handle unbinding one of two bound edges correctly

* Rename boundElement in state to startBoundElement

* Dont double account for zoom when rendering binding highlight

* Fix rendering of edited linear element point handles

* Suggest binding when adding new point to a linear element

* Bind when adding a new point to a linear element and dont unbind when moving middle elements

* Handle deleting points

* Add cmd modifier key to disable binding

* Use state for enabling binding, fix not binding for linear elements during creation

* Drop support for binding lines, only arrows are bindable

* Reset binding mode on blur

* Fix not binding lines

src/actions/actionDeleteSelected.tsx

@@ -11,6 +11,7 @@ import { AppState } from "../types";
 import { newElementWith } from "../element/mutateElement";
 import { getElementsInGroup } from "../groups";
 import { LinearElementEditor } from "../element/linearElementEditor";
+import { fixBindingsAfterDeletion } from "../element/binding";
 
 const deleteSelectedElements = (
   elements: readonly ExcalidrawElement[],
@@ -53,7 +54,12 @@ export const actionDeleteSelected = register({
   name: "deleteSelectedElements",
   perform: (elements, appState) => {
     if (appState.editingLinearElement) {
-      const { elementId, activePointIndex } = appState.editingLinearElement;
+      const {
+        elementId,
+        activePointIndex,
+        startBindingElement,
+        endBindingElement,
+      } = appState.editingLinearElement;
       const element = LinearElementEditor.getElement(elementId);
       if (!element) {
         return false;
@@ -62,7 +68,7 @@ export const actionDeleteSelected = register({
         // case: no point selected → delete whole element
         activePointIndex == null ||
         activePointIndex === -1 ||
-        // case: deleting last point
+        // case: deleting last remaining point
         element.points.length < 2
       ) {
         const nextElements = elements.filter((el) => el.id !== element.id);
@@ -78,6 +84,17 @@ export const actionDeleteSelected = register({
         };
       }
 
+      // We cannot do this inside `movePoint` because it is also called
+      // when deleting the uncommitted point (which hasn't caused any binding)
+      const binding = {
+        startBindingElement:
+          activePointIndex === 0 ? null : startBindingElement,
+        endBindingElement:
+          activePointIndex === element.points.length - 1
+            ? null
+            : endBindingElement,
+      };
+
       LinearElementEditor.movePoint(element, activePointIndex, "delete");
 
       return {
@@ -86,6 +103,7 @@ export const actionDeleteSelected = register({
           ...appState,
           editingLinearElement: {
             ...appState.editingLinearElement,
+            ...binding,
             activePointIndex: activePointIndex > 0 ? activePointIndex - 1 : 0,
           },
         },
@@ -97,6 +115,10 @@ export const actionDeleteSelected = register({
       elements: nextElements,
       appState: nextAppState,
     } = deleteSelectedElements(elements, appState);
+    fixBindingsAfterDeletion(
+      nextElements,
+      elements.filter(({ id }) => appState.selectedElementIds[id]),
+    );
 
     nextAppState = handleGroupEditingState(nextAppState, nextElements);