perf: make eraser great again (#9352)

* perf: make eraser great again

* lint

* refactor and improve perf

* lint

packages/excalidraw/eraser/index.ts

@@ -0,0 +1,239 @@
+import { arrayToMap, easeOut, THEME } from "@excalidraw/common";
+import { getElementLineSegments } from "@excalidraw/element/bounds";
+import {
+  lineSegment,
+  lineSegmentIntersectionPoints,
+  pointFrom,
+} from "@excalidraw/math";
+
+import { getElementsInGroup } from "@excalidraw/element/groups";
+
+import { getElementShape } from "@excalidraw/element/shapes";
+import { shouldTestInside } from "@excalidraw/element/collision";
+import { isPointInShape } from "@excalidraw/utils/collision";
+import {
+  hasBoundTextElement,
+  isBoundToContainer,
+} from "@excalidraw/element/typeChecks";
+import { getBoundTextElementId } from "@excalidraw/element/textElement";
+
+import type { GeometricShape } from "@excalidraw/utils/shape";
+import type {
+  ElementsSegmentsMap,
+  GlobalPoint,
+  LineSegment,
+} from "@excalidraw/math/types";
+import type { ExcalidrawElement } from "@excalidraw/element/types";
+
+import { AnimatedTrail } from "../animated-trail";
+
+import type { AnimationFrameHandler } from "../animation-frame-handler";
+
+import type App from "../components/App";
+
+// just enough to form a segment; this is sufficient for eraser
+const POINTS_ON_TRAIL = 2;
+
+export class EraserTrail extends AnimatedTrail {
+  private elementsToErase: Set<ExcalidrawElement["id"]> = new Set();
+  private groupsToErase: Set<ExcalidrawElement["id"]> = new Set();
+  private segmentsCache: Map<string, LineSegment<GlobalPoint>[]> = new Map();
+  private geometricShapesCache: Map<string, GeometricShape<GlobalPoint>> =
+    new Map();
+
+  constructor(animationFrameHandler: AnimationFrameHandler, app: App) {
+    super(animationFrameHandler, app, {
+      streamline: 0.2,
+      size: 5,
+      keepHead: true,
+      sizeMapping: (c) => {
+        const DECAY_TIME = 200;
+        const DECAY_LENGTH = 10;
+        const t = Math.max(
+          0,
+          1 - (performance.now() - c.pressure) / DECAY_TIME,
+        );
+        const l =
+          (DECAY_LENGTH -
+            Math.min(DECAY_LENGTH, c.totalLength - c.currentIndex)) /
+          DECAY_LENGTH;
+
+        return Math.min(easeOut(l), easeOut(t));
+      },
+      fill: () =>
+        app.state.theme === THEME.LIGHT
+          ? "rgba(0, 0, 0, 0.2)"
+          : "rgba(255, 255, 255, 0.2)",
+    });
+  }
+
+  startPath(x: number, y: number): void {
+    this.endPath();
+    super.startPath(x, y);
+    this.elementsToErase.clear();
+  }
+
+  addPointToPath(x: number, y: number, restore = false) {
+    super.addPointToPath(x, y);
+
+    const elementsToEraser = this.updateElementsToBeErased(restore);
+
+    return elementsToEraser;
+  }
+
+  private updateElementsToBeErased(restoreToErase?: boolean) {
+    let eraserPath: GlobalPoint[] =
+      super
+        .getCurrentTrail()
+        ?.originalPoints?.map((p) => pointFrom<GlobalPoint>(p[0], p[1])) || [];
+
+    // for efficiency and avoid unnecessary calculations,
+    // take only POINTS_ON_TRAIL points to form some number of segments
+    eraserPath = eraserPath?.slice(eraserPath.length - POINTS_ON_TRAIL);
+
+    const visibleElementsMap = arrayToMap(this.app.visibleElements);
+
+    const pathSegments = eraserPath.reduce((acc, point, index) => {
+      if (index === 0) {
+        return acc;
+      }
+      acc.push(lineSegment(eraserPath[index - 1], point));
+      return acc;
+    }, [] as LineSegment<GlobalPoint>[]);
+
+    if (pathSegments.length === 0) {
+      return [];
+    }
+
+    for (const element of this.app.visibleElements) {
+      // restore only if already added to the to-be-erased set
+      if (restoreToErase && this.elementsToErase.has(element.id)) {
+        const intersects = eraserTest(
+          pathSegments,
+          element,
+          this.segmentsCache,
+          this.geometricShapesCache,
+          visibleElementsMap,
+          this.app,
+        );
+
+        if (intersects) {
+          const shallowestGroupId = element.groupIds.at(-1)!;
+
+          if (this.groupsToErase.has(shallowestGroupId)) {
+            const elementsInGroup = getElementsInGroup(
+              this.app.scene.getNonDeletedElementsMap(),
+              shallowestGroupId,
+            );
+            for (const elementInGroup of elementsInGroup) {
+              this.elementsToErase.delete(elementInGroup.id);
+            }
+            this.groupsToErase.delete(shallowestGroupId);
+          }
+
+          if (isBoundToContainer(element)) {
+            this.elementsToErase.delete(element.containerId);
+          }
+
+          if (hasBoundTextElement(element)) {
+            const boundText = getBoundTextElementId(element);
+
+            if (boundText) {
+              this.elementsToErase.delete(boundText);
+            }
+          }
+
+          this.elementsToErase.delete(element.id);
+        }
+      } else if (!restoreToErase && !this.elementsToErase.has(element.id)) {
+        const intersects = eraserTest(
+          pathSegments,
+          element,
+          this.segmentsCache,
+          this.geometricShapesCache,
+          visibleElementsMap,
+          this.app,
+        );
+
+        if (intersects) {
+          const shallowestGroupId = element.groupIds.at(-1)!;
+
+          if (!this.groupsToErase.has(shallowestGroupId)) {
+            const elementsInGroup = getElementsInGroup(
+              this.app.scene.getNonDeletedElementsMap(),
+              shallowestGroupId,
+            );
+
+            for (const elementInGroup of elementsInGroup) {
+              this.elementsToErase.add(elementInGroup.id);
+            }
+            this.groupsToErase.add(shallowestGroupId);
+          }
+
+          if (hasBoundTextElement(element)) {
+            const boundText = getBoundTextElementId(element);
+
+            if (boundText) {
+              this.elementsToErase.add(boundText);
+            }
+          }
+
+          if (isBoundToContainer(element)) {
+            this.elementsToErase.add(element.containerId);
+          }
+
+          this.elementsToErase.add(element.id);
+        }
+      }
+    }
+
+    return Array.from(this.elementsToErase);
+  }
+
+  endPath(): void {
+    super.endPath();
+    super.clearTrails();
+    this.elementsToErase.clear();
+    this.groupsToErase.clear();
+    this.segmentsCache.clear();
+  }
+}
+
+const eraserTest = (
+  pathSegments: LineSegment<GlobalPoint>[],
+  element: ExcalidrawElement,
+  elementsSegments: ElementsSegmentsMap,
+  shapesCache = new Map<string, GeometricShape<GlobalPoint>>(),
+  visibleElementsMap = new Map<string, ExcalidrawElement>(),
+  app: App,
+): boolean => {
+  let shape = shapesCache.get(element.id);
+
+  if (!shape) {
+    shape = getElementShape<GlobalPoint>(element, visibleElementsMap);
+    shapesCache.set(element.id, shape);
+  }
+
+  const lastPoint = pathSegments[pathSegments.length - 1][1];
+  if (shouldTestInside(element) && isPointInShape(lastPoint, shape)) {
+    return true;
+  }
+
+  let elementSegments = elementsSegments.get(element.id);
+
+  if (!elementSegments) {
+    elementSegments = getElementLineSegments(element, visibleElementsMap);
+    elementsSegments.set(element.id, elementSegments);
+  }
+
+  return pathSegments.some((pathSegment) =>
+    elementSegments?.some(
+      (elementSegment) =>
+        lineSegmentIntersectionPoints(
+          pathSegment,
+          elementSegment,
+          app.getElementHitThreshold(),
+        ) !== null,
+    ),
+  );
+};