I’m reading Game Physics Engine Development by Ian Millington. It’s helping me figure out lots of collision and force related equations. However I still have a code problem this book isn’t helping to resolve. Let me break it down:

The game has a main cycle…

1. Update every object

2. Draw the result

3. Repeat

A problem occurs when an object applies force to another object and the second object appears to lag behind. What’s happening is that the lagging object was updated before the force applying object and as a result the lagging object doesn’t update until the next cycle. In this scenario the drawing function has been applied before it updates again and as a result it doesn’t reflect the new force.

I was thinking of several approaches:

1. Calculate any remaining force applications by adding a third aspect to the main game cycle at the end to make sure everything is up to date.

2. Create a “flag” in each object which tells an object whether to update or not and apply a second update while turning this flag off. I could have this flag automatically turned on again after every update.

3. My mind started to wonder about a contact resolver class and how I could implement something to mastermind all the physics equations.

EDIT:

I was able to fix this problem by keeping track of all the new forces and adding a third stage to the update process. During the original update stage all new forces are added to a list. After all the updating has been done, all the forces are taken care of. Thanks goes to h4tt3n for suggesting this was a good approach.

EDIT: This above is just an adhoc approach now that I’ve utilized and thought about it, it can be improved. Check back on this blog for an updated approach.

-James