Thanks

Did you by any chance get anywhere with a solution to this? Could you clarify what the end result was, if so? Was it worth it?

Rgds,

-Nick

As for the interpolation, you don’t want to do a partial physics step. You want to interpolate between the last two complete physics steps. Essentially you want to render your physics one frame in the past, at a delay of up to the size of the interval. I’ve never actually done it before, but I imagine it will not be accomplished without some amount of sweating.

I’ve reread the last bit of that ‘Fix your timestep’ a few times, and it seems like you make the game intentionally lag by the percentage of a frame that’s in the accumulator by interpolating between the previous frame and the current one. I can understand interpolating a simple straight vector movement from A to B, but it seems like such an approach would have a large number of special cases, which increase with the complexity of your physics. For example, an object is orbiting a point, if you just find the point half way between the previous and current position, that won’t be correct. You’d need to know that in that case, you’re finding half way between a certain amount of movement around a circle. And consider a case where you need to interpolate for an object’s frame based animation, movement vector and rotation of its graphic. I can’t think of a way to do that sort of thing in a generic manner.

This results in a fairly regular visual ‘jarring’ effect (which is more apparent on faster moving objects) on object movement, which doesn’t occur if you process the full accumulated amount per frame. Even with frame based, this is less of an issue as your FPS generally hovers around the same amount (assuming you cap it at a reasonable value, like 30fps).

The description on how to address this in the ‘Fix your timestep’ article is a bit cryptic, so I am still unsure as to how one solves this problem. Processing the remainder after all full intervals have been processed will solve the problem, but breaks the determinism. One could try and ‘temporarily’ apply the remainder of movement, then roll it back and process it in a full interval the next frame, but that sounds very messy to me, since you’d need to run all game logic just like a full interval, and you may have collisions which occur and set off a whole chain of events in the game. Do you have any suggestions on how to tackle this problem?