applyLinearImpulse method

@override void applyLinearImpulse(PhysicsBody body, double ix, double iy)

Apply an instantaneous change in momentum to body.

Unlike writing velocity directly this preserves existing motion, which is what knockback, bounce pads and explosions want.

Implementation

@override
void applyLinearImpulse(PhysicsBody body, double ix, double iy) {
  if (!_nativeReady) {
    super.applyLinearImpulse(body, ix, iy);
    return;
  }
  final b2Body = _bodyMap[body];
  if (b2Body == null || !body.isDynamic) return;

  b2Body.applyLinearImpulse(ix, iy);
  // Mirror the resulting velocity change into the Dart body as well.
  //
  // update() pushes body.velocity into native at the top of EVERY frame, so
  // an impulse applied between frames would be integrated by Box2D and then
  // immediately overwritten by the stale Dart value on the next push. The
  // impulse would appear to work for exactly one step and then vanish.
  body.velocity.x += ix * body.inverseMass;
  body.velocity.y += iy * body.inverseMass;
  body.isAwake = true;
  body.sleepTimer = 0.0;
}