Declare Path.transform and Path.toSVG and their tests

src/Path.test.ts

@@ -0,0 +1,20 @@
+import '../jest.setup'
+
+import {Path} from './Path'
+
+describe('Path', () => {
+	it('should compute `toSVG` correctly', () => {
+		const path: Path = [
+			['M', [0, 0]],
+			['L', [1, 1]],
+			['L', [2, 2]],
+			['Q', [3, 3], [4, 4]],
+			['A', [1, 1], 1, false, true, [5, 5]],
+			['Z'],
+		]
+
+		expect(Path.toSVG(path)).toEqual(
+			'M 0,0 L 1,1 L 2,2 Q 3,3 4,4 A 1,1 1 0 1 5,5 Z'
+		)
+	})
+})

src/Path.ts

@@ -1,4 +1,6 @@
-import {vec2} from 'linearly'
+import {mat2d, vec2} from 'linearly'
+
+import {toFixedSimple} from './utils'
 
 // Line commands
 export type CommandM = ['M', end: vec2]
@@ -37,4 +39,55 @@ export type Command =
 
 export type Path = Command[]
 
-export namespace Path {}
+export namespace Path {
+	export function transform(path: Path, matrix: mat2d): Path {
+		return path.map(([command, ...points]) => {
+			switch (command) {
+				case 'M':
+				case 'L':
+				case 'Q':
+				case 'T':
+				case 'C':
+				case 'S':
+					return [
+						command,
+						...(points as vec2[]).map(p => vec2.transformMat2d(p, matrix)),
+					]
+				case 'H':
+					return [
+						command,
+						vec2.transformMat2d([points[0] as number, 0], matrix)[0],
+					]
+				case 'V':
+					return [
+						command,
+						vec2.transformMat2d([0, points[0] as number], matrix)[0],
+					]
+				case 'A':
+					throw new Error('Not implemented')
+				case 'Z':
+					return ['Z']
+			}
+		}) as Path
+	}
+
+	export function toSVG(path: Path, fractionDigits = 2): string {
+		return path
+			.map(([command, ...ps]) => {
+				const strs = ps.map(p => {
+					if (typeof p === 'number') {
+						return toFixedSimple(p, fractionDigits)
+					} else if (typeof p === 'boolean') {
+						return p ? '1' : '0'
+					} else {
+						const x = toFixedSimple(p[0], fractionDigits)
+						const y = toFixedSimple(p[1], fractionDigits)
+						return `${x},${y}`
+					}
+				})
+
+				return [command, ...strs].join(' ')
+			})
+			.join(' ')
+	}
+}