feat: move rotation into dedicated file

Signed-off-by: André Jaenisch <andre.jaenisch@posteo.de>

src/js/rotation.js

@@ -0,0 +1,31 @@
+import { FPS } from './constants.js'
+import { computeNormals } from './shape.js'
+import { rotate } from './vector.js'
+
+/** @typedef {import('./shape').Shape} Shape */
+/** @typedef {import('./vector').Vector2D} Vector2D */
+
+/**
+ * Update the rotation of the shape.
+ *
+ * @param {Shape} shape
+ */
+export function updateRotation (shape) {
+  shape.v = shape.v + shape.a * 1 / FPS
+  rotateShape(shape, shape.v * 1 / FPS)
+}
+
+/**
+ * Rotate a shape around its centre.
+ *
+ * @param {Shape} shape
+ * @param {number} angle
+ */
+function rotateShape (shape, angle) {
+  shape.G = shape.G + angle
+
+  shape.X.forEach(function (vertex, index) {
+    shape.X[index] = rotate(vertex, shape.C, angle)
+    computeNormals(shape)
+  })
+}

test/js/rotation.test.js

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+import { expect } from 'chai'
+
+import { updateRotation } from '../../src/js/rotation.js'
+import { RigidShape } from '../../src/js/shape.js'
+import { Vec2 } from '../../src/js/vector.js'
+
+describe('Rotation', function () {
+  it('should update the rotation', function () {
+    // Arrange
+    const shape = makeShape()
+    const g = shape.G // angle
+    const v = shape.v // angle velocity
+    const x = [...shape.X]
+
+    // Act
+    updateRotation(shape)
+    
+    // Assert
+    expect(shape.G).to.equal(g)
+    expect(shape.v).to.equal(v)
+    shape.X.forEach(function (vertex, i) { expect(vertex).not.to.equal(x[i]) })
+  })
+})
+
+function makeShape () {
+  const center = Vec2(500, 200)
+  const friction = 20
+  const restitution = 0
+  const mass = 400
+  const bounds = 1
+  const width = 5
+  const height = 5
+
+  const shape = RigidShape({
+    center,
+    mass,
+    friction,
+    restitution,
+    bounds,
+    width,
+    height
+  })
+
+  return shape
+}

types/rotation.d.ts

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+/** @typedef {import('./shape').Shape} Shape */
+/** @typedef {import('./vector').Vector2D} Vector2D */
+/**
+ * Update the rotation of the shape.
+ *
+ * @param {Shape} shape
+ */
+export function updateRotation(shape: Shape): void;
+export type Shape = import('./shape').Shape;
+export type Vector2D = import('./vector').Vector2D;