Forums » Impact Engine » Questions about the engine

I was thinking about buying impact but I have a couple questions about the engine.

1. How do multiple levels get handled along with garbage collection? I see nothing relating to scenes or levels in the docs.

2. How is time stepping managed (especially with physics)? Previous frameworks I have used use delta time for certain things but generally not for physics. How is the rate set on the physics and how does it compare between mobile and desktop?

Level changing is easy. You can have a trigger in the game that when touched loads a new level. Put this invisible trigger over a door for example, and it loads the level name you either assign in the trigger or you can probably do it in code. Very easy.

Timers are also easy:

var myTimer = new ig.Timer(0.4); // will start counting up from -0.4 seconds

if ( this.myTimer.delta() > 0 ); // timer is up, but keeps counting

this.myTimer.set(0.4); // set back to -0.4 seconds

Not sure about physics engines. I haven't used Impact with Box2D but there are several examples of Impact using Box2D

To be more specific with question number 2 I'm wondering how velocity and acceleration get effected across platforms with variable framerates. If a game runs at 20fps on a mobile device and 80fps on a desktop will the actual movement be the same on both platforms or will the mobile game be slower?

A solution to this issue is often to multiply your character's movement by delta time (velocity = 100 * deltatime), but that usually does not work well with a physics engine.

All physics in Impact are calculated with a delta value (ig.system.tick) - the time since the last frame. For most tasks you don't have to deal with this delta yourself, but simply set a velocity or acceleration for an entity and the engine will do the rest.

This works well for Impact's built-in physics. I also haven't found any issues with Box2D using the same delta. I guess it works fine as long as the frame rate is relatively stable!?

The ig.Timer description details how edge cases (low fps) are handled.

Hiya Dominic. I'm working on an Impact+Box2D game. The framerate that is occasionally unstable, which can result is the player doing mega jumps. Is there anyway I can fix this?

Don't worry. I am going to try the suggestion in this thread: http://impactjs.com/forums/help/deterministic-game-loop

Thanks.