From 34ec751501ef1838ae73ffe611d7b989571972bf Mon Sep 17 00:00:00 2001
From: Mark Tolmacs <mark@lazycat.hu>
Date: Fri, 27 Sep 2024 20:27:10 +0200
Subject: [PATCH] Attempt at optimizing focus point calc

---
 packages/excalidraw/element/binding.ts | 58 +++++++++++++++++---------
 packages/math/point.ts                 | 14 +++++--
 packages/math/vector.ts                | 15 ++++++-
 3 files changed, 63 insertions(+), 24 deletions(-)

diff --git a/packages/excalidraw/element/binding.ts b/packages/excalidraw/element/binding.ts
index 8d3057c8e3..4a394a9cc6 100644
--- a/packages/excalidraw/element/binding.ts
+++ b/packages/excalidraw/element/binding.ts
@@ -73,6 +73,11 @@ import {
   pointDistanceSq,
   clamp,
   radians,
+  vectorScale,
+  pointFromVector,
+  vectorRotate,
+  vectorNormalize,
+  pointDistance,
 } from "../../math";
 import { segmentIntersectRectangleElement } from "../../utils/geometry/shape";
 import { distanceToBindableElement } from "./distance";
@@ -1425,7 +1430,7 @@ const determineFocusPoint = (
     GAPoint.from(adjecentPoint),
   );
   const reverseRelateToCenter = GA.reverse(relateToCenter);
-  let point;
+  let p: GA.Point;
   switch (element.type) {
     case "rectangle":
     case "image":
@@ -1435,14 +1440,18 @@ const determineFocusPoint = (
     case "embeddable":
     case "frame":
     case "magicframe":
-      point = findFocusPointForRectangulars(element, focus, adjecentPointRel);
+      p = findFocusPointForRectanguloidElement(
+        element,
+        focus,
+        adjecentPointRel,
+      );
       break;
     case "ellipse":
-      point = findFocusPointForEllipse(element, focus, adjecentPointRel);
+      p = findFocusPointForEllipse(element, focus, adjecentPointRel);
       break;
   }
   return pointFromPair(
-    GAPoint.toTuple(GATransform.apply(reverseRelateToCenter, point)),
+    GAPoint.toTuple(GATransform.apply(reverseRelateToCenter, p)),
   );
 };
 
@@ -1692,7 +1701,7 @@ const findFocusPointForEllipse = (
   return GA.point(x, (-m * x - 1) / n);
 };
 
-const findFocusPointForRectangulars = (
+const findFocusPointForRectanguloidElement = (
   element:
     | ExcalidrawRectangleElement
     | ExcalidrawImageElement
@@ -1705,23 +1714,34 @@ const findFocusPointForRectangulars = (
   relativeDistance: number,
   // The point for which we're trying to find the focus point, relative
   // to the element center.
-  point: GA.Point,
+  gaPoint: GA.Point,
 ): GA.Point => {
-  const relativeDistanceAbs = Math.abs(relativeDistance);
-  const orientation = Math.sign(relativeDistance);
-  const corners = getCorners(element, relativeDistanceAbs);
+  const relP = pointFromPair<GlobalPoint>(GAPoint.toTuple(gaPoint));
+  const center = point<GlobalPoint>(
+    element.x + element.width / 2,
+    element.y + element.height / 2,
+  );
+  const p = point<GlobalPoint>(center[0] + relP[0], center[1] + relP[1]);
+  const ret = pointFromVector(
+    vectorScale(
+      vectorRotate(
+        vectorNormalize(vectorFromPoint(p, center)),
+        radians(Math.PI / 2),
+      ),
+      Math.sign(relativeDistance) *
+        Math.min(
+          pointDistance(point<GlobalPoint>(element.x, element.y), center) *
+            Math.abs(relativeDistance),
+          element.width / 2,
+          element.height / 2,
+        ),
+    ),
+    center,
+  );
 
-  let maxDistance = 0;
-  let tangentPoint: null | GA.Point = null;
-  corners.forEach((corner) => {
-    const distance = orientation * GALine.through(point, corner)[1];
-    if (distance > maxDistance) {
-      maxDistance = distance;
-      tangentPoint = corner;
-    }
-  });
-  return tangentPoint!;
+  return GA.point(ret[0] - center[0], ret[1] - center[1]);
 };
+
 export const bindingProperties: Set<BindableProp | BindingProp> = new Set([
   "boundElements",
   "frameId",
diff --git a/packages/math/point.ts b/packages/math/point.ts
index 471eab8765..bdfdfbeaac 100644
--- a/packages/math/point.ts
+++ b/packages/math/point.ts
@@ -46,8 +46,11 @@ export function pointFromPair<Point extends GenericPoint>(
  * @param v The vector to convert
  * @returns The point the vector points at with origin 0,0
  */
-export function pointFromVector<P extends GenericPoint>(v: Vector): P {
-  return v as unknown as P;
+export function pointFromVector<P extends GenericPoint>(
+  v: Vector,
+  offset: P = point(0, 0),
+): P {
+  return point<P>(offset[0] + v[0], offset[1] + v[1]);
 }
 
 /**
@@ -96,9 +99,12 @@ export function pointRotateRads<Point extends GenericPoint>(
   [cx, cy]: Point,
   angle: Radians,
 ): Point {
+  const cos = Math.cos(angle);
+  const sin = Math.sin(angle);
+
   return point(
-    (x - cx) * Math.cos(angle) - (y - cy) * Math.sin(angle) + cx,
-    (x - cx) * Math.sin(angle) + (y - cy) * Math.cos(angle) + cy,
+    (x - cx) * cos - (y - cy) * sin + cx,
+    (x - cx) * sin + (y - cy) * cos + cy,
   );
 }
 
diff --git a/packages/math/vector.ts b/packages/math/vector.ts
index d987ea1b00..17620adaf8 100644
--- a/packages/math/vector.ts
+++ b/packages/math/vector.ts
@@ -1,4 +1,4 @@
-import type { GenericPoint, Vector } from "./types";
+import type { GenericPoint, Radians, Vector } from "./types";
 
 /**
  * Create a vector from the x and y coordiante elements.
@@ -139,3 +139,16 @@ export const vectorNormalize = (v: Vector): Vector => {
 
   return vector(v[0] / m, v[1] / m);
 };
+
+/**
+ * Rotate a vector by the given radians
+ * @param v Target vector
+ * @param a Angle to rotate in radians
+ * @returns The rotated vector
+ */
+export const vectorRotate = (v: Vector, a: Radians): Vector => {
+  const cos = Math.cos(a);
+  const sin = Math.sin(a);
+
+  return vector(v[0] * cos - v[1] * sin, v[0] * sin + v[1] * cos);
+};