Cleaner initial state on gravity reset

src/index.ts

@@ -139,7 +139,6 @@ function evolveSystem(state: State, dt: number) {
   correctEnergy(state);
 
   // to prevent floating point overflow, we clamp theta between [0, PI*2]
-
   if (Math.abs(state.system.theta) > Math.PI * 2) {
     const sign = state.system.theta > 0 ? -1 : 1;
     state.system.theta +=
@@ -148,13 +147,6 @@ function evolveSystem(state: State, dt: number) {
 }
 
 function update(state: State) {
-  if (state.system.theta == null) {
-    state.system.theta = INITIAL_THETA;
-  }
-  if (state.system.angularVelocity == null) {
-    state.system.angularVelocity = INITIAL_ANGULAR_VELOCITY;
-  }
-
   let dt = state.dt;
   while (dt > 0) {
     const expectedFrameTime = 16 + 2 / 3;
@@ -167,25 +159,30 @@ function update(state: State) {
 const canvas = <HTMLCanvasElement>document.getElementById("canvas");
 const engine = new Engine(canvas);
 
-const loop = (state: State, ctx: CanvasRenderingContext2D) => {
-  update(state);
-  draw(state, ctx);
-  engine.nextFrame(loop);
-};
-engine.nextFrame(loop);
-window.requestAnimationFrame(engine.run.bind(engine));
-
 const energyInput = new Input("Energy", String(INITIAL_ENERGY), (e?: Event) => {
   engine.state.system.energy = energyInput.getValue();
 });
-engine.state.system.energy = energyInput.getValue();
 
 const gravityInput = new Input(
   "Gravity",
   String(INITIAL_GRAVITY),
   (e?: Event) => {
     engine.state.system.gravity = gravityInput.getValue();
+    engine.state.system.angularVelocity = INITIAL_ANGULAR_VELOCITY;
+    engine.state.system.theta = INITIAL_THETA;
     energyInput.setValue(getCurrentEnergy(engine.state));
   }
 );
+
+engine.state.system.energy = energyInput.getValue();
 engine.state.system.gravity = gravityInput.getValue();
+engine.state.system.theta = INITIAL_THETA;
+engine.state.system.angularVelocity = INITIAL_ANGULAR_VELOCITY;
+
+const loop = (state: State, ctx: CanvasRenderingContext2D) => {
+  update(state);
+  draw(state, ctx);
+  engine.nextFrame(loop);
+};
+engine.nextFrame(loop);
+window.requestAnimationFrame(engine.run.bind(engine));