How to make interactions between bouncy objects more consistent

[notnullnotvoid]

This gif shows the situation I'm running into. The boxes all have a restitution coefficient of 0.9. In the case on the right, where the lower box is resting stationary on the floor, it seems like most of the energy disappears in the collision. The interaction on the left is more like what I'd expect, but the amount of bounce you get is very sensitive to whether the bottom box happens to be touching the ground at the exact moment when the two boxes collide.

Is there any way to make these kinds of multi-body interactions more consistent in general, so that the restitution isn't dampened so much in the case on the right?

[notnullnotvoid]

I did some testing with Box2D 2.4, and the results were a lot more consistent. Here's a similar setup but with the restitution at 1.0 instead of 0.9:

There's still a bit of energy lost in the collision, but the box bounces almost all the way back to its original height. I know Box2D 3 uses a different solver, so maybe it's not a straightforward thing to fix, but I'm wondering if there's still a way to get something like the old behavior in the new version.

[erincatto]

It is possible to make the restitution algorithm iterate to get better accuracy. You can fork and try it.
See b2ApplyOverflowRestitution and B2_FORCE_OVERFLOW. This will be slow. Look for these lines:

		// it is possible to get more accurate restitution by iterating
		// this only makes a difference if there are two contact points
		for (int iter = 0; iter < 2; ++iter)

In general I recommend people don't switch to 3.0 for games that have shipped already because the behavior is different.

[notnullnotvoid]

Adding the iteration loop doesn't seem change the outcome in any way that I can notice. Setting B2_FORCE_OVERFLOW to 1 does change the behavior, but only slightly.