snapshot of https://github.com/excalidraw/excalidraw.git (master, 2026-09-16; blobs > 131072B omitted)

packages/excalidraw/eraser/index.ts

@@ -0,0 +1,304 @@
+import { arrayToMap, easeOut, THEME } from "@excalidraw/common";
+
+import {
+  computeBoundTextPosition,
+  doBoundsIntersect,
+  getBoundTextElement,
+  getElementBounds,
+  getElementLineSegments,
+  getFreedrawOutlineAsSegments,
+  getFreedrawOutlinePoints,
+  intersectElementWithLineSegment,
+  isArrowElement,
+  isFreeDrawElement,
+  isLineElement,
+  isPointInElement,
+} from "@excalidraw/element";
+import {
+  lineSegment,
+  lineSegmentsDistance,
+  pointFrom,
+  polygon,
+  polygonIncludesPointNonZero,
+} from "@excalidraw/math";
+
+import { getElementsInGroup } from "@excalidraw/element";
+
+import { shouldTestInside } from "@excalidraw/element";
+import { hasBoundTextElement, isBoundToContainer } from "@excalidraw/element";
+import { getBoundTextElementId } from "@excalidraw/element";
+
+import type { Bounds } from "@excalidraw/common";
+
+import type { GlobalPoint, LineSegment } from "@excalidraw/math/types";
+import type { ElementsMap, ExcalidrawElement } from "@excalidraw/element/types";
+
+import { AnimatedTrail } from "../animatedTrail";
+
+import type App from "../components/App";
+
+export class EraserTrail extends AnimatedTrail {
+  private elementsToErase: Set<ExcalidrawElement["id"]> = new Set();
+  private groupsToErase: Set<ExcalidrawElement["id"]> = new Set();
+
+  constructor(app: App) {
+    super(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) {
+    const eraserPath: GlobalPoint[] =
+      super
+        .getCurrentTrail()
+        ?.originalPoints?.map((p) => pointFrom<GlobalPoint>(p[0], p[1])) || [];
+
+    if (eraserPath.length < 2) {
+      return [];
+    }
+
+    // for efficiency and avoid unnecessary calculations,
+    // take only POINTS_ON_TRAIL points to form some number of segments
+    const pathSegment = lineSegment<GlobalPoint>(
+      eraserPath[eraserPath.length - 1],
+      eraserPath[eraserPath.length - 2],
+    );
+
+    const candidateElements = this.app.visibleElements.filter(
+      (el) => !el.locked,
+    );
+
+    const candidateElementsMap = arrayToMap(candidateElements);
+
+    for (const element of candidateElements) {
+      // restore only if already added to the to-be-erased set
+      if (restoreToErase && this.elementsToErase.has(element.id)) {
+        const intersects = eraserTest(
+          pathSegment,
+          element,
+          candidateElementsMap,
+          this.app.state.zoom.value,
+        );
+
+        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(
+          pathSegment,
+          element,
+          candidateElementsMap,
+          this.app.state.zoom.value,
+        );
+
+        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();
+  }
+}
+
+const eraserTest = (
+  pathSegment: LineSegment<GlobalPoint>,
+  element: ExcalidrawElement,
+  elementsMap: ElementsMap,
+  zoom: number,
+): boolean => {
+  const lastPoint = pathSegment[1];
+
+  // PERF: Do a quick bounds intersection test first because it's cheap
+  const threshold = isFreeDrawElement(element) ? 15 : element.strokeWidth / 2;
+  const segmentBounds = [
+    Math.min(pathSegment[0][0], pathSegment[1][0]) - threshold,
+    Math.min(pathSegment[0][1], pathSegment[1][1]) - threshold,
+    Math.max(pathSegment[0][0], pathSegment[1][0]) + threshold,
+    Math.max(pathSegment[0][1], pathSegment[1][1]) + threshold,
+  ] as Bounds;
+  const origElementBounds = getElementBounds(element, elementsMap);
+  const elementBounds: Bounds = [
+    origElementBounds[0] - threshold,
+    origElementBounds[1] - threshold,
+    origElementBounds[2] + threshold,
+    origElementBounds[3] + threshold,
+  ];
+
+  if (!doBoundsIntersect(segmentBounds, elementBounds)) {
+    return false;
+  }
+
+  // There are shapes where the inner area should trigger erasing
+  // even though the eraser path segment doesn't intersect with or
+  // get close to the shape's stroke
+  if (
+    shouldTestInside(element) &&
+    isPointInElement(lastPoint, element, elementsMap)
+  ) {
+    return true;
+  }
+
+  // Freedraw elements are tested for erasure by measuring the distance
+  // of the eraser path and the freedraw shape outline lines to a tolerance
+  // which offers a good visual precision at various zoom levels
+  if (isFreeDrawElement(element)) {
+    const outlinePoints = getFreedrawOutlinePoints(element);
+    const strokeSegments = getFreedrawOutlineAsSegments(
+      element,
+      outlinePoints,
+      elementsMap,
+    );
+    const tolerance = Math.max(2.25, 5 / zoom); // NOTE: Visually fine-tuned approximation
+
+    for (const seg of strokeSegments) {
+      if (lineSegmentsDistance(seg, pathSegment) <= tolerance) {
+        return true;
+      }
+    }
+
+    const poly = polygon(
+      ...(outlinePoints.map(([x, y]) =>
+        pointFrom<GlobalPoint>(element.x + x, element.y + y),
+      ) as GlobalPoint[]),
+    );
+
+    // PERF: Check only one point of the eraser segment. If the eraser segment
+    // start is inside the closed freedraw shape, the other point is either also
+    // inside or the eraser segment will intersect the shape outline anyway
+    if (polygonIncludesPointNonZero(pathSegment[0], poly)) {
+      return true;
+    }
+
+    return false;
+  }
+
+  const boundTextElement = getBoundTextElement(element, elementsMap);
+
+  if (isArrowElement(element) || (isLineElement(element) && !element.polygon)) {
+    const tolerance = Math.max(
+      element.strokeWidth,
+      (element.strokeWidth * 2) / zoom,
+    );
+
+    // If the eraser movement is so fast that a large distance is covered
+    // between the last two points, the distanceToElement miss, so we test
+    // agaist each segment of the linear element
+    const segments = getElementLineSegments(element, elementsMap);
+    for (const seg of segments) {
+      if (lineSegmentsDistance(seg, pathSegment) <= tolerance) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  return (
+    intersectElementWithLineSegment(element, elementsMap, pathSegment, 0, true)
+      .length > 0 ||
+    (!!boundTextElement &&
+      intersectElementWithLineSegment(
+        {
+          ...boundTextElement,
+          ...computeBoundTextPosition(element, boundTextElement, elementsMap),
+        },
+        elementsMap,
+        pathSegment,
+        0,
+        true,
+      ).length > 0)
+  );
+};