1 files changed, 202 insertions, 0 deletions
diff --git a/packages/excalidraw/element/heading.ts b/packages/excalidraw/element/heading.ts
new file mode 100644
index 0000000..94e8633
--- /dev/null
+++ b/packages/excalidraw/element/heading.ts
@@ -0,0 +1,202 @@
+import type {
+  LocalPoint,
+  GlobalPoint,
+  Triangle,
+  Vector,
+  Radians,
+} from "@excalidraw/math";
+import {
+  pointFrom,
+  pointRotateRads,
+  pointScaleFromOrigin,
+  radiansToDegrees,
+  triangleIncludesPoint,
+  vectorFromPoint,
+} from "@excalidraw/math";
+import { getCenterForBounds, type Bounds } from "./bounds";
+import type { ExcalidrawBindableElement } from "./types";
+
+export const HEADING_RIGHT = [1, 0] as Heading;
+export const HEADING_DOWN = [0, 1] as Heading;
+export const HEADING_LEFT = [-1, 0] as Heading;
+export const HEADING_UP = [0, -1] as Heading;
+export type Heading = [1, 0] | [0, 1] | [-1, 0] | [0, -1];
+
+export const headingForDiamond = <Point extends GlobalPoint | LocalPoint>(
+  a: Point,
+  b: Point,
+) => {
+  const angle = radiansToDegrees(
+    Math.atan2(b[1] - a[1], b[0] - a[0]) as Radians,
+  );
+  if (angle >= 315 || angle < 45) {
+    return HEADING_UP;
+  } else if (angle >= 45 && angle < 135) {
+    return HEADING_RIGHT;
+  } else if (angle >= 135 && angle < 225) {
+    return HEADING_DOWN;
+  }
+  return HEADING_LEFT;
+};
+
+export const vectorToHeading = (vec: Vector): Heading => {
+  const [x, y] = vec;
+  const absX = Math.abs(x);
+  const absY = Math.abs(y);
+  if (x > absY) {
+    return HEADING_RIGHT;
+  } else if (x <= -absY) {
+    return HEADING_LEFT;
+  } else if (y > absX) {
+    return HEADING_DOWN;
+  }
+  return HEADING_UP;
+};
+
+export const headingForPoint = <P extends GlobalPoint | LocalPoint>(
+  p: P,
+  o: P,
+) => vectorToHeading(vectorFromPoint<P>(p, o));
+
+export const headingForPointIsHorizontal = <P extends GlobalPoint | LocalPoint>(
+  p: P,
+  o: P,
+) => headingIsHorizontal(headingForPoint<P>(p, o));
+
+export const compareHeading = (a: Heading, b: Heading) =>
+  a[0] === b[0] && a[1] === b[1];
+
+export const headingIsHorizontal = (a: Heading) =>
+  compareHeading(a, HEADING_RIGHT) || compareHeading(a, HEADING_LEFT);
+
+export const headingIsVertical = (a: Heading) => !headingIsHorizontal(a);
+
+// Gets the heading for the point by creating a bounding box around the rotated
+// close fitting bounding box, then creating 4 search cones around the center of
+// the external bbox.
+export const headingForPointFromElement = <
+  Point extends GlobalPoint | LocalPoint,
+>(
+  element: Readonly<ExcalidrawBindableElement>,
+  aabb: Readonly<Bounds>,
+  p: Readonly<Point>,
+): Heading => {
+  const SEARCH_CONE_MULTIPLIER = 2;
+
+  const midPoint = getCenterForBounds(aabb);
+
+  if (element.type === "diamond") {
+    if (p[0] < element.x) {
+      return HEADING_LEFT;
+    } else if (p[1] < element.y) {
+      return HEADING_UP;
+    } else if (p[0] > element.x + element.width) {
+      return HEADING_RIGHT;
+    } else if (p[1] > element.y + element.height) {
+      return HEADING_DOWN;
+    }
+
+    const top = pointRotateRads(
+      pointScaleFromOrigin(
+        pointFrom(element.x + element.width / 2, element.y),
+        midPoint,
+        SEARCH_CONE_MULTIPLIER,
+      ),
+      midPoint,
+      element.angle,
+    );
+    const right = pointRotateRads(
+      pointScaleFromOrigin(
+        pointFrom(element.x + element.width, element.y + element.height / 2),
+        midPoint,
+        SEARCH_CONE_MULTIPLIER,
+      ),
+      midPoint,
+      element.angle,
+    );
+    const bottom = pointRotateRads(
+      pointScaleFromOrigin(
+        pointFrom(element.x + element.width / 2, element.y + element.height),
+        midPoint,
+        SEARCH_CONE_MULTIPLIER,
+      ),
+      midPoint,
+      element.angle,
+    );
+    const left = pointRotateRads(
+      pointScaleFromOrigin(
+        pointFrom(element.x, element.y + element.height / 2),
+        midPoint,
+        SEARCH_CONE_MULTIPLIER,
+      ),
+      midPoint,
+      element.angle,
+    );
+
+    if (
+      triangleIncludesPoint<Point>([top, right, midPoint] as Triangle<Point>, p)
+    ) {
+      return headingForDiamond(top, right);
+    } else if (
+      triangleIncludesPoint<Point>(
+        [right, bottom, midPoint] as Triangle<Point>,
+        p,
+      )
+    ) {
+      return headingForDiamond(right, bottom);
+    } else if (
+      triangleIncludesPoint<Point>(
+        [bottom, left, midPoint] as Triangle<Point>,
+        p,
+      )
+    ) {
+      return headingForDiamond(bottom, left);
+    }
+
+    return headingForDiamond(left, top);
+  }
+
+  const topLeft = pointScaleFromOrigin(
+    pointFrom(aabb[0], aabb[1]),
+    midPoint,
+    SEARCH_CONE_MULTIPLIER,
+  ) as Point;
+  const topRight = pointScaleFromOrigin(
+    pointFrom(aabb[2], aabb[1]),
+    midPoint,
+    SEARCH_CONE_MULTIPLIER,
+  ) as Point;
+  const bottomLeft = pointScaleFromOrigin(
+    pointFrom(aabb[0], aabb[3]),
+    midPoint,
+    SEARCH_CONE_MULTIPLIER,
+  ) as Point;
+  const bottomRight = pointScaleFromOrigin(
+    pointFrom(aabb[2], aabb[3]),
+    midPoint,
+    SEARCH_CONE_MULTIPLIER,
+  ) as Point;
+
+  return triangleIncludesPoint<Point>(
+    [topLeft, topRight, midPoint] as Triangle<Point>,
+    p,
+  )
+    ? HEADING_UP
+    : triangleIncludesPoint<Point>(
+        [topRight, bottomRight, midPoint] as Triangle<Point>,
+        p,
+      )
+    ? HEADING_RIGHT
+    : triangleIncludesPoint<Point>(
+        [bottomRight, bottomLeft, midPoint] as Triangle<Point>,
+        p,
+      )
+    ? HEADING_DOWN
+    : HEADING_LEFT;
+};
+
+export const flipHeading = (h: Heading): Heading =>
+  [
+    h[0] === 0 ? 0 : h[0] > 0 ? -1 : 1,
+    h[1] === 0 ? 0 : h[1] > 0 ? -1 : 1,
+  ] as Heading;