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/element/bounds.ts

@@ -10,11 +10,14 @@ import {
 import { isLinearElement } from "./typeChecks";
 import { rescalePoints } from "../points";
 
+// x and y position of top left corner, x and y position of bottom right corner
+export type Bounds = readonly [number, number, number, number];
+
 // If the element is created from right to left, the width is going to be negative
 // This set of functions retrieves the absolute position of the 4 points.
 export const getElementAbsoluteCoords = (
   element: ExcalidrawElement,
-): [number, number, number, number] => {
+): Bounds => {
   if (isLinearElement(element)) {
     return getLinearElementAbsoluteCoords(element);
   }
@@ -26,6 +29,13 @@ export const getElementAbsoluteCoords = (
   ];
 };
 
+export const pointRelativeTo = (
+  element: ExcalidrawElement,
+  absoluteCoords: Point,
+): Point => {
+  return [absoluteCoords[0] - element.x, absoluteCoords[1] - element.y];
+};
+
 export const getDiamondPoints = (element: ExcalidrawElement) => {
   // Here we add +1 to avoid these numbers to be 0
   // otherwise rough.js will throw an error complaining about it
@@ -35,7 +45,7 @@ export const getDiamondPoints = (element: ExcalidrawElement) => {
   const rightY = Math.floor(element.height / 2) + 1;
   const bottomX = topX;
   const bottomY = element.height;
-  const leftX = topY;
+  const leftX = 0;
   const leftY = rightY;
 
   return [topX, topY, rightX, rightY, bottomX, bottomY, leftX, leftY];