Torque and Motors

␣

Hold to thrust

game.ts

const renderLayers = {
  foreground: 1 << 0,
};

export const createTorqueGame = async (): Promise<Game> => {
  const { game, world, renderContext, time } = createGame('demo-game');

  createCamera(world, {
    isStatic: true,
    cullingMask: renderLayers.foreground,
    verticalWorldUnits: DEMO_VERTICAL_WORLD_UNITS,
  });

  // No gravity system is registered: these flywheels only ever spin in
  // place, so nothing needs to pull them downward.
  const thrustInput = new HoldAction('thrust');
  const inputManager = registerInputs(world, time, {
    holdActions: [thrustInput],
  });
  const keyboardInputSource = new KeyboardInputSource(inputManager);

  keyboardInputSource.holdBindings.add(
    new KeyboardHoldBinding(thrustInput, keyCodes.space),
  );

  const { x: width, y: height } = calculateVisibleWorldSize(
    renderContext.width,
    renderContext.height,
    DEMO_VERTICAL_WORLD_UNITS,
  );
  const columnWidth = width / 2;

  await createThrusterScenario(
    world,
    renderContext,
    renderLayers.foreground,
    { x: -columnWidth / 2, y: height * 0.1 },
    thrustInput,
  );

  await createMotorScenario(world, renderContext, renderLayers.foreground, {
    x: columnWidth / 2,
    y: height * 0.1,
  });

  // `createThrusterEcsSystem` and `createGustEcsSystem` change
  // `RigidBodyEcsComponent.angularVelocity` directly for this tick, and
  // `createAngularVelocityMotorEcsSystem` reads/corrects it, so all three
  // must run before whatever system integrates velocity into position
  // (`createEulerIntegrationEcsSystem`).
  world.addSystem(createThrusterEcsSystem(time));
  world.addSystem(createGustEcsSystem(time));
  world.addSystem(createAngularVelocityMotorEcsSystem(time));
  world.addSystem(createCameraEcsSystem(time));
  world.addSystem(createRenderEcsSystem(renderContext));
  world.addSystem(createEulerIntegrationEcsSystem(time));

  return game;
};

This demo showcases the two ways to spin a RigidBody with torque. On the left, a flywheel carries a demo-specific ThrusterEcsComponent: while Space is held, createThrusterEcsSystem calls RigidBody.applyTorque on it directly every tick, spinning it up, and releasing lets a small angularDrag on the body gradually spin it back down, since nothing drives it once the torque stops. There's no engine-provided component for this one-shot/manual case, a game is expected to write a small system like this itself. On the right, a flywheel carries an AngularVelocityMotorEcsComponent, a built-in engine component that holds a steady target angular velocity on its own, no input needed, with no angularDrag of its own; a demo-only gust periodically knocks its speed off course, and the motor spends its limited maxTorque budget correcting back towards the target every tick afterwards.