Fix Arc.transform

src/Arc.test.ts

@@ -2,6 +2,7 @@ import {mat2d, vec2} from 'linearly'
 import {describe, expect, it, test} from 'vitest'
 
 import {Arc} from './Arc'
+import {SegmentA} from './Segment'
 
 describe('toCenterParameterization', () => {
 	it('should work in right angle case', () => {
@@ -300,3 +301,23 @@ describe('ellipticArcLength', () => {
 		expect(ret).toEqual(1.01218)
 	})
 })
+
+describe('transform', () => {
+	const arc: SegmentA = {
+		command: 'A',
+		start: [50, 0],
+		point: [0, 25],
+		args: [[50, 25], 0, false, true],
+	}
+
+	it('should rotate 90°', () => {
+		const ret = Arc.transform(arc, mat2d.rotation(90))
+
+		expect(ret).toEqual({
+			command: 'A',
+			start: [0, 50],
+			point: [-25, 0],
+			args: [[50, 25], 90, false, true],
+		})
+	})
+})

src/Arc.ts

@@ -275,7 +275,7 @@ export namespace Arc {
 
 				A2 = 0.5 * (A + C + K * ac)
 				C2 = 0.5 * (A + C - K * ac)
-				offsetRot = 0.5 * scalar.atan(B, ac)
+				offsetRot = scalar.deg(0.5 * Math.atan2(B, ac))
 			}
 		}
 
@@ -286,8 +286,8 @@ export namespace Arc {
 
 		// now A2 and C2 are half-axis:
 		if (ac <= 0) {
-			rv = C2
-			rh = A2
+			rv = A2
+			rh = C2
 		} else {
 			rv = C2
 			rh = A2