Feature: Multi Point Arrows (#338)

* Add points to arrow on double click

* Use line generator instead of path to generate line segments

* Switch color of the circle when it is on an existing point in the segment

* Check point against both ends of the line segment to find collinearity

* Keep drawing the arrow based on mouse position until shape is changed

* Always select the arrow when in multi element mode

* Use curves instead of lines when drawing arrow points

* Add basic collision detection with some debug points

* Use roughjs shape when performing hit testing

* Draw proper handler rectangles for arrows

* Add argument to renderScene in export

* Globally resize all points on the arrow when bounds are resized

* Hide handler rectangles if an arrow has no size

- Allow continuing adding arrows when selected element is deleted

* Add dragging functionality to arrows

* Add SHIFT functionality to two point arrows

- Fix arrow positions when scrolling
- Revert the element back to selection when not in multi select mode

* Clean app state for export (JSON)

* Set curve options manually instead of using global options

- For some reason, this fixed the flickering issue in all shapes when arrows are rendered

* Set proper options for the arrow

* Increaase accuracy of hit testing arrows

- Additionally, skip testing if point is outside the domain of arrow and each curve

* Calculate bounding box of arrow based on roughjs curves

- Remove domain check per curve

* Change bounding box threshold to 10 and remove unnecessary code

* Fix handler rectangles for 2 and multi point arrows

- Fix margins of handler rectangles when using arrows
- Show handler rectangles in endpoints of 2-point arrows

* Remove unnecessary values from app state for export

* Use `resetTransform` instead of "retranslating" canvas space after each element rendering

* Allow resizing 2-point arrows

- Fix position of one of the handler rectangles

* refactor variable initialization

* Refactored to extract out mult-point generation to the abstracted function

* prevent dragging on arrow creation if under threshold

* Finalize selection during multi element mode when ENTER or ESC is clicked

* Set dragging element to null when finalizing

* Remove pathSegmentCircle from code

* Check if element is any "non-value" instead of NULL

* Show two points on any two point arrow and fix visibility of arrows during scroll

* Resume recording when done with drawing

- When deleting a multi select element, revert back to selection element type

* Resize arrow starting points perfectly

* Fix direction of arrow resize based for NW

* Resume recording history when there is more than one arrow

* Set dragging element to NULL when element is not locked

* Blur active element when finalizing

* Disable undo/redo for multielement, editingelement, and resizing element

- Allow undoing parts of the arrow

* Disable element visibility for arrow

* Use points array for arrow bounds when bezier curve shape is not available

Co-authored-by: David Luzar <luzar.david@gmail.com>
Co-authored-by: Preet <833927+pshihn@users.noreply.github.com>

src/element/collision.ts

@@ -2,11 +2,13 @@ import { distanceBetweenPointAndSegment } from "../math";
 
 import { ExcalidrawElement } from "./types";
 import {
-  getArrowPoints,
   getDiamondPoints,
   getElementAbsoluteCoords,
   getLinePoints,
+  getArrowAbsoluteBounds,
 } from "./bounds";
+import { Point } from "roughjs/bin/geometry";
+import { Drawable, OpSet } from "roughjs/bin/core";
 
 function isElementDraggableFromInside(element: ExcalidrawElement): boolean {
   return element.backgroundColor !== "transparent" || element.isSelected;
@@ -145,18 +147,25 @@ export function hitTest(
         lineThreshold
     );
   } else if (element.type === "arrow") {
-    let [x1, y1, x2, y2, x3, y3, x4, y4] = getArrowPoints(element);
-    // The computation is done at the origin, we need to add a translation
-    x -= element.x;
-    y -= element.y;
+    if (!element.shape) {
+      return false;
+    }
+    const shape = element.shape as Drawable[];
+    // If shape does not consist of curve and two line segments
+    // for arrow shape, return false
+    if (shape.length < 3) return false;
 
+    const [x1, y1, x2, y2] = getArrowAbsoluteBounds(element);
+    if (x < x1 || y < y1 - 10 || x > x2 || y > y2 + 10) return false;
+
+    const relX = x - element.x;
+    const relY = y - element.y;
+
+    // hit test curve and lien segments for arrow
     return (
-      //    \
-      distanceBetweenPointAndSegment(x, y, x3, y3, x2, y2) < lineThreshold ||
-      // -----
-      distanceBetweenPointAndSegment(x, y, x1, y1, x2, y2) < lineThreshold ||
-      //    /
-      distanceBetweenPointAndSegment(x, y, x4, y4, x2, y2) < lineThreshold
+      hitTestRoughShape(shape[0].sets, relX, relY) ||
+      hitTestRoughShape(shape[1].sets, relX, relY) ||
+      hitTestRoughShape(shape[2].sets, relX, relY)
     );
   } else if (element.type === "line") {
     const [x1, y1, x2, y2] = getLinePoints(element);
@@ -176,3 +185,82 @@ export function hitTest(
     throw new Error("Unimplemented type " + element.type);
   }
 }
+
+const pointInBezierEquation = (
+  p0: Point,
+  p1: Point,
+  p2: Point,
+  p3: Point,
+  [mx, my]: Point,
+) => {
+  // B(t) = p0 * (1-t)^3 + 3p1 * t * (1-t)^2 + 3p2 * t^2 * (1-t) + p3 * t^3
+  const equation = (t: number, idx: number) =>
+    Math.pow(1 - t, 3) * p3[idx] +
+    3 * t * Math.pow(1 - t, 2) * p2[idx] +
+    3 * Math.pow(t, 2) * (1 - t) * p1[idx] +
+    p0[idx] * Math.pow(t, 3);
+
+  const epsilon = 20;
+  // go through t in increments of 0.01
+  let t = 0;
+  while (t <= 1.0) {
+    const tx = equation(t, 0);
+    const ty = equation(t, 1);
+
+    const diff = Math.sqrt(Math.pow(tx - mx, 2) + Math.pow(ty - my, 2));
+
+    if (diff < epsilon) {
+      return true;
+    }
+
+    t += 0.01;
+  }
+
+  return false;
+};
+
+const hitTestRoughShape = (opSet: OpSet[], x: number, y: number) => {
+  // read operations from first opSet
+  const ops = opSet[0].ops;
+
+  // set start position as (0,0) just in case
+  // move operation does not exist (unlikely but it is worth safekeeping it)
+  let currentP: Point = [0, 0];
+
+  return ops.some(({ op, data }, idx) => {
+    // There are only four operation types:
+    // move, bcurveTo, lineTo, and curveTo
+    if (op === "move") {
+      // change starting point
+      currentP = data as Point;
+      // move operation does not draw anything; so, it always
+      // returns false
+    } else if (op === "bcurveTo") {
+      // create points from bezier curve
+      // bezier curve stores data as a flattened array of three positions
+      // [x1, y1, x2, y2, x3, y3]
+      const p1 = [data[0], data[1]] as Point;
+      const p2 = [data[2], data[3]] as Point;
+      const p3 = [data[4], data[5]] as Point;
+
+      const p0 = currentP;
+      currentP = p3;
+
+      // check if points are on the curve
+      // cubic bezier curves require four parameters
+      // the first parameter is the last stored position (p0)
+      let retVal = pointInBezierEquation(p0, p1, p2, p3, [x, y]);
+
+      // set end point of bezier curve as the new starting point for
+      // upcoming operations as each operation is based on the last drawn
+      // position of the previous operation
+      return retVal;
+    } else if (op === "lineTo") {
+      // TODO: Implement this
+    } else if (op === "qcurveTo") {
+      // TODO: Implement this
+    }
+
+    return false;
+  });
+};