feat: show a mid point for linear elements (#5534)

* feat: Add a mid point for linear elements

* fix tests

* show mid point only on hover

* hacky fix :(

* don't add mid points if present and only add outside editor

* improve styling and always show phantom point instead of just on hover

* fix tests

* fix

* only add polyfill for test

* add hover state for phantom point

* fix tests

* fix

* Add Array.at polyfill

* reuse `centerPoint()` helper

* reuse `distance2d`

* use `Point` type

Co-authored-by: dwelle <luzar.david@gmail.com>

src/components/App.tsx

@@ -1,5 +1,6 @@
 import React, { useContext } from "react";
 import { flushSync } from "react-dom";
+
 import { RoughCanvas } from "roughjs/bin/canvas";
 import rough from "roughjs/bin/rough";
 import clsx from "clsx";
@@ -3030,6 +3031,7 @@ class App extends React.Component<AppProps, AppState> {
     }
     if (this.state.selectedLinearElement) {
       let hoverPointIndex = -1;
+      let midPointHovered = false;
       if (
         isHittingElementNotConsideringBoundingBox(element, this.state, [
           scenePointerX,
@@ -3042,7 +3044,13 @@ class App extends React.Component<AppProps, AppState> {
           scenePointerX,
           scenePointerY,
         );
-        if (hoverPointIndex >= 0) {
+        midPointHovered = LinearElementEditor.isHittingMidPoint(
+          linearElementEditor,
+          { x: scenePointerX, y: scenePointerY },
+          this.state,
+        );
+
+        if (hoverPointIndex >= 0 || midPointHovered) {
           setCursor(this.canvas, CURSOR_TYPE.POINTER);
         } else {
           setCursor(this.canvas, CURSOR_TYPE.MOVE);
@@ -3069,6 +3077,17 @@ class App extends React.Component<AppProps, AppState> {
           },
         });
       }
+
+      if (
+        this.state.selectedLinearElement.midPointHovered !== midPointHovered
+      ) {
+        this.setState({
+          selectedLinearElement: {
+            ...this.state.selectedLinearElement,
+            midPointHovered,
+          },
+        });
+      }
     } else {
       setCursor(this.canvas, CURSOR_TYPE.AUTO);
     }
@@ -3623,7 +3642,7 @@ class App extends React.Component<AppProps, AppState> {
               this.setState({ editingLinearElement: ret.linearElementEditor });
             }
           }
-          if (ret.didAddPoint) {
+          if (ret.didAddPoint && !ret.isMidPoint) {
             return true;
           }
         }
@@ -4112,6 +4131,7 @@ class App extends React.Component<AppProps, AppState> {
       // to ensure we don't create a 2-point arrow by mistake when
       // user clicks mouse in a way that it moves a tiny bit (thus
       // triggering pointermove)
+
       if (
         !pointerDownState.drag.hasOccurred &&
         (this.state.activeTool.type === "arrow" ||
@@ -4128,7 +4148,6 @@ class App extends React.Component<AppProps, AppState> {
           return;
         }
       }
-
       if (pointerDownState.resize.isResizing) {
         pointerDownState.lastCoords.x = pointerCoords.x;
         pointerDownState.lastCoords.y = pointerCoords.y;
@@ -4339,8 +4358,10 @@ class App extends React.Component<AppProps, AppState> {
         }
 
         if (points.length === 1) {
-          mutateElement(draggingElement, { points: [...points, [dx, dy]] });
-        } else if (points.length > 1) {
+          mutateElement(draggingElement, {
+            points: [...points, [dx, dy]],
+          });
+        } else if (points.length === 2) {
           mutateElement(draggingElement, {
             points: [...points.slice(0, -1), [dx, dy]],
           });
@@ -6202,4 +6223,5 @@ if (
     },
   });
 }
+
 export default App;

src/element/linearElementEditor.ts

@@ -11,6 +11,7 @@ import {
   isPathALoop,
   getGridPoint,
   rotatePoint,
+  centerPoint,
 } from "../math";
 import { getElementAbsoluteCoords, getLockedLinearCursorAlignSize } from ".";
 import { getElementPointsCoords } from "./bounds";
@@ -51,6 +52,7 @@ export class LinearElementEditor {
     | "keep";
   public readonly endBindingElement: ExcalidrawBindableElement | null | "keep";
   public readonly hoverPointIndex: number;
+  public readonly midPointHovered: boolean;
 
   constructor(element: NonDeleted<ExcalidrawLinearElement>, scene: Scene) {
     this.elementId = element.id as string & {
@@ -70,6 +72,7 @@ export class LinearElementEditor {
       lastClickedPoint: -1,
     };
     this.hoverPointIndex = -1;
+    this.midPointHovered = false;
   }
 
   // ---------------------------------------------------------------------------
@@ -157,7 +160,6 @@ export class LinearElementEditor {
     if (!linearElementEditor) {
       return false;
     }
-
     const { selectedPointsIndices, elementId } = linearElementEditor;
     const element = LinearElementEditor.getElement(elementId);
     if (!element) {
@@ -357,6 +359,59 @@ export class LinearElementEditor {
     };
   }
 
+  static isHittingMidPoint = (
+    linearElementEditor: LinearElementEditor,
+    scenePointer: { x: number; y: number },
+    appState: AppState,
+  ) => {
+    if (appState.editingLinearElement) {
+      return false;
+    }
+    const { elementId } = linearElementEditor;
+    const element = LinearElementEditor.getElement(elementId);
+    if (!element) {
+      return false;
+    }
+    const clickedPointIndex = LinearElementEditor.getPointIndexUnderCursor(
+      element,
+      appState.zoom,
+      scenePointer.x,
+      scenePointer.y,
+    );
+    if (clickedPointIndex >= 0) {
+      return false;
+    }
+    const points = LinearElementEditor.getPointsGlobalCoordinates(element);
+    if (points.length >= 3) {
+      return false;
+    }
+
+    const midPoint = this.getMidPoint(linearElementEditor);
+    if (midPoint) {
+      const threshold =
+        LinearElementEditor.POINT_HANDLE_SIZE / appState.zoom.value;
+      const distance = distance2d(
+        midPoint[0],
+        midPoint[1],
+        scenePointer.x,
+        scenePointer.y,
+      );
+      return distance <= threshold;
+    }
+    return false;
+  };
+
+  static getMidPoint(linearElementEditor: LinearElementEditor) {
+    const { elementId } = linearElementEditor;
+    const element = LinearElementEditor.getElement(elementId);
+    if (!element) {
+      return null;
+    }
+    const points = LinearElementEditor.getPointsGlobalCoordinates(element);
+
+    return centerPoint(points[0], points.at(-1)!);
+  }
+
   static handlePointerDown(
     event: React.PointerEvent<HTMLCanvasElement>,
     appState: AppState,
@@ -367,11 +422,13 @@ export class LinearElementEditor {
     didAddPoint: boolean;
     hitElement: NonDeleted<ExcalidrawElement> | null;
     linearElementEditor: LinearElementEditor | null;
+    isMidPoint: boolean;
   } {
     const ret: ReturnType<typeof LinearElementEditor["handlePointerDown"]> = {
       didAddPoint: false,
       hitElement: null,
       linearElementEditor: null,
+      isMidPoint: false,
     };
 
     if (!linearElementEditor) {
@@ -384,6 +441,45 @@ export class LinearElementEditor {
     if (!element) {
       return ret;
     }
+    const hittingMidPoint = LinearElementEditor.isHittingMidPoint(
+      linearElementEditor,
+      scenePointer,
+      appState,
+    );
+    if (
+      LinearElementEditor.isHittingMidPoint(
+        linearElementEditor,
+        scenePointer,
+        appState,
+      )
+    ) {
+      const midPoint = this.getMidPoint(linearElementEditor);
+      if (midPoint) {
+        mutateElement(element, {
+          points: [
+            element.points[0],
+            LinearElementEditor.createPointAt(
+              element,
+              midPoint[0],
+              midPoint[1],
+              appState.gridSize,
+            ),
+            ...element.points.slice(1),
+          ],
+        });
+      }
+      ret.didAddPoint = true;
+      ret.isMidPoint = true;
+      ret.linearElementEditor = {
+        ...linearElementEditor,
+        selectedPointsIndices: element.points[1],
+        pointerDownState: {
+          prevSelectedPointsIndices: linearElementEditor.selectedPointsIndices,
+          lastClickedPoint: -1,
+        },
+        lastUncommittedPoint: null,
+      };
+    }
     if (event.altKey && appState.editingLinearElement) {
       if (linearElementEditor.lastUncommittedPoint == null) {
         mutateElement(element, {
@@ -397,6 +493,7 @@ export class LinearElementEditor {
             ),
           ],
         });
+        ret.didAddPoint = true;
       }
       history.resumeRecording();
       ret.linearElementEditor = {
@@ -426,7 +523,7 @@ export class LinearElementEditor {
 
     // if we clicked on a point, set the element as hitElement otherwise
     // it would get deselected if the point is outside the hitbox area
-    if (clickedPointIndex > -1) {
+    if (clickedPointIndex >= 0 || hittingMidPoint) {
       ret.hitElement = element;
     } else {
       // You might be wandering why we are storing the binding elements on
@@ -567,14 +664,14 @@ export class LinearElementEditor {
   /** scene coords */
   static getPointsGlobalCoordinates(
     element: NonDeleted<ExcalidrawLinearElement>,
-  ) {
+  ): Point[] {
     const [x1, y1, x2, y2] = getElementAbsoluteCoords(element);
     const cx = (x1 + x2) / 2;
     const cy = (y1 + y2) / 2;
     return element.points.map((point) => {
       let { x, y } = element;
       [x, y] = rotate(x + point[0], y + point[1], cx, cy, element.angle);
-      return [x, y];
+      return [x, y] as const;
     });
   }
 

src/excalidraw-app/index.tsx

@@ -1,3 +1,4 @@
+import polyfill from "../polyfill";
 import LanguageDetector from "i18next-browser-languagedetector";
 import { useCallback, useEffect, useRef, useState } from "react";
 import { trackEvent } from "../analytics";
@@ -83,6 +84,7 @@ import { jotaiStore, useAtomWithInitialValue } from "../jotai";
 import { reconcileElements } from "./collab/reconciliation";
 import { parseLibraryTokensFromUrl, useHandleLibrary } from "../data/library";
 
+polyfill();
 window.EXCALIDRAW_THROTTLE_RENDER = true;
 
 const isExcalidrawPlusSignedUser = document.cookie.includes(

src/packages/excalidraw/entry.js

@@ -1,5 +1,7 @@
 import "./publicPath";
+import polyfill from "../../polyfill";
 
 import "../../../public/fonts.css";
 
+polyfill();
 export * from "./index";

src/packages/excalidraw/index.tsx

@@ -1,5 +1,4 @@
 import React, { useEffect, forwardRef } from "react";
-
 import { InitializeApp } from "../../components/InitializeApp";
 import App from "../../components/App";
 

src/polyfill.ts

@@ -0,0 +1,26 @@
+const polyfill = () => {
+  if (!Array.prototype.at) {
+    // Taken from https://github.com/tc39/proposal-relative-indexing-method#polyfill so that it works in tests
+    /* eslint-disable */
+    Object.defineProperty(Array.prototype, "at", {
+      value: function (n: number) {
+        // ToInteger() abstract op
+        n = Math.trunc(n) || 0;
+        // Allow negative indexing from the end
+        if (n < 0) {
+          n += this.length;
+        }
+        // OOB access is guaranteed to return undefined
+        if (n < 0 || n >= this.length) {
+          return undefined;
+        }
+        // Otherwise, this is just normal property access
+        return this[n];
+      },
+      writable: true,
+      enumerable: false,
+      configurable: true,
+    });
+  }
+};
+export default polyfill;

src/renderer/renderScene.ts

@@ -2,7 +2,7 @@ import { RoughCanvas } from "roughjs/bin/canvas";
 import { RoughSVG } from "roughjs/bin/svg";
 import oc from "open-color";
 
-import { AppState, BinaryFiles, Zoom } from "../types";
+import { AppState, BinaryFiles, Point, Zoom } from "../types";
 import {
   ExcalidrawElement,
   NonDeletedExcalidrawElement,
@@ -157,34 +157,105 @@ const strokeGrid = (
   context.restore();
 };
 
+const renderSingleLinearPoint = (
+  context: CanvasRenderingContext2D,
+  appState: AppState,
+  renderConfig: RenderConfig,
+  point: Point,
+  isSelected: boolean,
+  isPhantomPoint = false,
+) => {
+  context.strokeStyle = "#5e5ad8";
+  context.setLineDash([]);
+  context.fillStyle = "rgba(255, 255, 255, 0.9)";
+  if (isSelected) {
+    context.fillStyle = "rgba(134, 131, 226, 0.9)";
+  } else if (isPhantomPoint) {
+    context.fillStyle = "rgba(177, 151, 252, 0.7)";
+  }
+  const { POINT_HANDLE_SIZE } = LinearElementEditor;
+  const radius = appState.editingLinearElement
+    ? POINT_HANDLE_SIZE
+    : POINT_HANDLE_SIZE / 2;
+  fillCircle(
+    context,
+    point[0],
+    point[1],
+    radius / renderConfig.zoom.value,
+    !isPhantomPoint,
+  );
+};
+
 const renderLinearPointHandles = (
   context: CanvasRenderingContext2D,
   appState: AppState,
   renderConfig: RenderConfig,
   element: NonDeleted<ExcalidrawLinearElement>,
 ) => {
+  if (!appState.selectedLinearElement) {
+    return;
+  }
   context.save();
   context.translate(renderConfig.scrollX, renderConfig.scrollY);
   context.lineWidth = 1 / renderConfig.zoom.value;
-
-  LinearElementEditor.getPointsGlobalCoordinates(element).forEach(
-    (point, idx) => {
-      context.strokeStyle = "#5e5ad8";
-      context.setLineDash([]);
-      context.fillStyle =
-        appState.editingLinearElement?.selectedPointsIndices?.includes(idx)
-          ? "rgba(134, 131, 226, 0.9)"
-          : "rgba(255, 255, 255, 0.9)";
-      const { POINT_HANDLE_SIZE } = LinearElementEditor;
-      const radius = appState.editingLinearElement
-        ? POINT_HANDLE_SIZE
-        : POINT_HANDLE_SIZE / 2;
-      fillCircle(context, point[0], point[1], radius / renderConfig.zoom.value);
-    },
+  const points = LinearElementEditor.getPointsGlobalCoordinates(element);
+  const centerPoint = LinearElementEditor.getMidPoint(
+    appState.selectedLinearElement,
   );
+  if (!centerPoint) {
+    return;
+  }
+  points.forEach((point, idx) => {
+    const isSelected =
+      !!appState.editingLinearElement?.selectedPointsIndices?.includes(idx);
+    renderSingleLinearPoint(context, appState, renderConfig, point, isSelected);
+  });
+
+  if (!appState.editingLinearElement && points.length < 3) {
+    if (appState.selectedLinearElement.midPointHovered) {
+      const centerPoint = LinearElementEditor.getMidPoint(
+        appState.selectedLinearElement,
+      )!;
+      highlightPoint(centerPoint, context, appState, renderConfig);
+
+      renderSingleLinearPoint(
+        context,
+        appState,
+        renderConfig,
+        centerPoint,
+        false,
+      );
+    } else {
+      renderSingleLinearPoint(
+        context,
+        appState,
+        renderConfig,
+        centerPoint,
+        false,
+        true,
+      );
+    }
+  }
+
   context.restore();
 };
 
+const highlightPoint = (
+  point: Point,
+  context: CanvasRenderingContext2D,
+  appState: AppState,
+  renderConfig: RenderConfig,
+) => {
+  context.fillStyle = "rgba(105, 101, 219, 0.4)";
+
+  fillCircle(
+    context,
+    point[0],
+    point[1],
+    LinearElementEditor.POINT_HANDLE_SIZE / renderConfig.zoom.value,
+    false,
+  );
+};
 const renderLinearElementPointHighlight = (
   context: CanvasRenderingContext2D,
   appState: AppState,
@@ -202,23 +273,14 @@ const renderLinearElementPointHighlight = (
   if (!element) {
     return;
   }
-  const [x, y] = LinearElementEditor.getPointAtIndexGlobalCoordinates(
+  const point = LinearElementEditor.getPointAtIndexGlobalCoordinates(
     element,
     hoverPointIndex,
   );
   context.save();
   context.translate(renderConfig.scrollX, renderConfig.scrollY);
 
-  context.fillStyle = "rgba(105, 101, 219, 0.4)";
-
-  fillCircle(
-    context,
-    x,
-    y,
-    LinearElementEditor.POINT_HANDLE_SIZE / renderConfig.zoom.value,
-    false,
-  );
-
+  highlightPoint(point, context, appState, renderConfig);
   context.restore();
 };
 
@@ -345,7 +407,7 @@ export const _renderScene = (
 
   if (
     appState.selectedLinearElement &&
-    appState.selectedLinearElement.hoverPointIndex !== -1
+    appState.selectedLinearElement.hoverPointIndex >= 0
   ) {
     renderLinearElementPointHighlight(context, appState, renderConfig);
   }

src/setupTests.ts

@@ -1,8 +1,9 @@
 import "@testing-library/jest-dom";
 import "jest-canvas-mock";
-
 import dotenv from "dotenv";
+import polyfill from "./polyfill";
 
+polyfill();
 // jest doesn't know of .env.development so we need to init it ourselves
 dotenv.config({
   path: require("path").resolve(__dirname, "../.env.development"),

src/tests/__snapshots__/regressionTests.test.tsx.snap

@@ -10982,6 +10982,7 @@ Object {
     "hoverPointIndex": -1,
     "isDragging": false,
     "lastUncommittedPoint": null,
+    "midPointHovered": false,
     "pointerDownState": Object {
       "lastClickedPoint": -1,
       "prevSelectedPointsIndices": null,
@@ -11207,6 +11208,7 @@ Object {
     "hoverPointIndex": -1,
     "isDragging": false,
     "lastUncommittedPoint": null,
+    "midPointHovered": false,
     "pointerDownState": Object {
       "lastClickedPoint": -1,
       "prevSelectedPointsIndices": null,
@@ -11659,6 +11661,7 @@ Object {
     "hoverPointIndex": -1,
     "isDragging": false,
     "lastUncommittedPoint": null,
+    "midPointHovered": false,
     "pointerDownState": Object {
       "lastClickedPoint": -1,
       "prevSelectedPointsIndices": null,
@@ -12063,6 +12066,7 @@ Object {
     "hoverPointIndex": -1,
     "isDragging": false,
     "lastUncommittedPoint": null,
+    "midPointHovered": false,
     "pointerDownState": Object {
       "lastClickedPoint": -1,
       "prevSelectedPointsIndices": null,

src/tests/__snapshots__/selection.test.tsx.snap

@@ -21,6 +21,10 @@ Object {
       0,
       0,
     ],
+    Array [
+      15,
+      25,
+    ],
     Array [
       30,
       50,
@@ -36,8 +40,8 @@ Object {
   "strokeWidth": 1,
   "type": "arrow",
   "updated": 1,
-  "version": 3,
-  "versionNonce": 449462985,
+  "version": 4,
+  "versionNonce": 453191,
   "width": 30,
   "x": 10,
   "y": 10,
@@ -65,6 +69,10 @@ Object {
       0,
       0,
     ],
+    Array [
+      15,
+      25,
+    ],
     Array [
       30,
       50,
@@ -80,8 +88,8 @@ Object {
   "strokeWidth": 1,
   "type": "line",
   "updated": 1,
-  "version": 3,
-  "versionNonce": 449462985,
+  "version": 4,
+  "versionNonce": 453191,
   "width": 30,
   "x": 10,
   "y": 10,