@tldraw/editor/src/lib/primitives/utils.test.ts

tldraw infinite canvas SDK (editor).

import { getPointInArcT } from './utils'

describe('getPointInArcT', () => {
	it('should return 0 for the start of the arc', () => {
		const mAB = Math.PI / 2 // 90 degrees
		const A = 0 // Start angle
		const B = Math.PI / 2 // End angle
		const P = 0 // Point angle, same as start
		expect(getPointInArcT(mAB, A, B, P)).toBe(0)
	})

	it('should return 1 for the end of the arc', () => {
		const mAB = Math.PI / 2 // 90 degrees
		const A = 0 // Start angle
		const B = Math.PI / 2 // End angle
		const P = Math.PI / 2 // Point angle, same as end
		expect(getPointInArcT(mAB, A, B, P)).toBe(1)
	})

	it('should return 0.5 for the midpoint of the arc', () => {
		const mAB = Math.PI // 180 degrees
		const A = 0 // Start angle
		const B = Math.PI // End angle
		const P = Math.PI / 2 // Point angle, midpoint
		expect(getPointInArcT(mAB, A, B, P)).toBe(0.5)
	})

	it('should handle negative arcs correctly', () => {
		const mAB = -Math.PI / 2 // -90 degrees, counter-clockwise
		const A = Math.PI / 2 // Start angle
		const B = 0 // End angle
		const P = Math.PI / 4 // Point angle, quarter way
		expect(getPointInArcT(mAB, A, B, P)).toBe(0.5)
	})

	it('should return correct t value for arcs larger than PI', () => {
		const mAB = Math.PI * 1.5 // 270 degrees
		const A = 0 // Start angle
		const B = -Math.PI / 2 // End angle, going counter-clockwise
		const P = -Math.PI / 4 // Point angle, halfway
		expect(getPointInArcT(mAB, A, B, P)).toBe(7 / 6)
	})

	it('should handle edge case where measurement to center is negative but measure to points near the end are positive', () => {
		const mAB = -2.8 // Arc measure
		const A = 0 // Start angle
		const B = 2.2 // End angle
		const P = 1.1 // Point angle, should be near the end
		expect(getPointInArcT(mAB, A, B, P)).toBe(0)
	})

	it('should handle edge case where measurement to center is negative but measure to points near the end are positive with other endpoint', () => {
		const mAB = 0 // Arc measure
		const A = 0 // Start angle
		const B = 2.2 // End angle
		const P = 1.1 // Point angle, should be near the end
		expect(getPointInArcT(mAB, A, B, P)).toBe(1)
	})
})