fix: flipping and resizing arrows (#979)

* fix: flipping horizontal for arrows

* fix: horizontal flip

* fix return

* add test for flipping arrow

* visualize arc points

* adding test for vertically flipping

* remove arc points

Co-authored-by: Steve Ruiz <steveruizok@gmail.com>

packages/tldraw/src/state/commands/flipShapes/flipShapes.spec.ts

@@ -1,5 +1,5 @@
 import { TldrawTestApp, mockDocument } from '~test'
-import type { RectangleShape } from '~types'
+import { ArrowShape, RectangleShape, TDShapeType } from '~types'
 
 describe('Flip command', () => {
   const app = new TldrawTestApp()
@@ -107,4 +107,70 @@ describe('Flip command', () => {
     expect(app.getShape<RectangleShape>('rect1').point).toStrictEqual([0, 0])
     expect(app.getShape<RectangleShape>('rect2').point).toStrictEqual([100, 100])
   })
+  it('flip curved arrow horizontally', () => {
+    app.createShapes({
+      id: 'arrow1',
+      type: TDShapeType.Arrow,
+      bend: -0.5464405676717543,
+      handles: {
+        start: {
+          bindingId: undefined,
+          canBind: true,
+          id: 'start',
+          index: 0,
+          point: [-13, 107],
+        },
+        end: {
+          bindingId: undefined,
+          canBind: true,
+          id: 'end',
+          index: 1,
+          point: [388, 112],
+        },
+        bend: {
+          id: 'bend',
+          index: 2,
+          point: [185, -0],
+        },
+      },
+      point: [1877, 677],
+    })
+    app.select('arrow1')
+    app.flipHorizontal()
+    expect(app.getShape<ArrowShape>('arrow1').point).toStrictEqual([1864, 677.19])
+    expect(app.getShape<ArrowShape>('arrow1').handles.bend.point).toStrictEqual([214.87, 219.06])
+  })
+  it('flip arrow vertically', () => {
+    app.createShapes({
+      id: 'arrow1',
+      type: TDShapeType.Arrow,
+      bend: -0.5464405676717543,
+      handles: {
+        start: {
+          bindingId: undefined,
+          canBind: true,
+          id: 'start',
+          index: 0,
+          point: [-13, 107],
+        },
+        end: {
+          bindingId: undefined,
+          canBind: true,
+          id: 'end',
+          index: 1,
+          point: [388, 112],
+        },
+        bend: {
+          id: 'bend',
+          index: 2,
+          point: [185, -0],
+        },
+      },
+      point: [1877, 677],
+    })
+    app.select('arrow1')
+    app.flipVertical()
+    expect(app.getShape<ArrowShape>('arrow1').point).toStrictEqual([1864, 677.19])
+    expect(app.getShape<ArrowShape>('arrow1').handles.bend.point).toStrictEqual([186.13, -107.25])
+  })
 })

packages/tldraw/src/state/shapes/ArrowUtil/ArrowUtil.tsx

@@ -376,7 +376,10 @@ export class ArrowUtil extends TDShapeUtil<T, E> {
     const initialShapeBounds = this.getBounds(initialShape)
     const handles: (keyof T['handles'])[] = ['start', 'end']
     const nextHandles = { ...initialShape.handles }
+
     handles.forEach((handle) => {
+      if (handle === 'bend') return
+
       const [x, y] = nextHandles[handle].point
       const nw = x / initialShapeBounds.width
       const nh = y / initialShapeBounds.height
@@ -388,19 +391,22 @@ export class ArrowUtil extends TDShapeUtil<T, E> {
         ],
       }
     })
-    const { start, bend, end } = nextHandles
-    const dist = Vec.dist(start.point, end.point)
-    const midPoint = Vec.med(start.point, end.point)
-    const bendDist = (dist / 2) * initialShape.bend
-    const u = Vec.uni(Vec.vec(start.point, end.point))
-    const point = Vec.add(midPoint, Vec.mul(Vec.per(u), bendDist))
-    nextHandles['bend'] = {
-      ...bend,
-      point: Vec.toFixed(Math.abs(bendDist) < 10 ? midPoint : point),
-    }
+
+    // If we've flipped one of the dimensions (but not both) then invert shape.bend
+
+    const nextBend =
+      (scaleX > 0 && scaleY < 0) || (scaleX < 0 && scaleY > 0)
+        ? -initialShape.bend
+        : initialShape.bend
+
+    // Find the position of the bend handle based on the new start / end handles and the new bend
+    const bendPoint = getBendPoint(nextHandles, nextBend)
+    nextHandles.bend.point = bendPoint
+
     return {
       point: Vec.toFixed([bounds.minX, bounds.minY]),
       handles: nextHandles,
+      bend: nextBend, // does this change?
     }
   }
 

packages/tldraw/src/state/shapes/ArrowUtil/arrowHelpers.ts

@@ -195,8 +195,9 @@ export function getArcPoints(start: number[], bend: number[], end: number[]) {
   const radius = circle[2]
   const startAngle = Vec.angle(center, start)
   const endAngle = Vec.angle(center, end)
-  for (let i = 1 / 20; i < 1; i += 1 / 20) {
-    const angle = Utils.lerpAngles(startAngle, endAngle, i)
+  for (let i = 0; i < 20; i++) {
+    const t = i / 19
+    const angle = Utils.lerpAngles(startAngle, endAngle, t)
     points.push(Vec.nudgeAtAngle(center, angle, radius))
   }
   return points