More Havok, Less Trauma

Originally posted to on April 2nd, 2008

On Monday and Tuesday, Havok 4 was implemented across the SL main grid. H4 is a major upgrade to the physics engine that’s critical for many things in Second Life, including sailboats.

This morning Vin Mariani and I did a few “first look” tests to check out how boats handle collisions on the main grid under H4.

H4 Bounce!
I’m sure you know the problem. You’re in the middle of a race and someone tacks in front of you. You try to veer away but your boat catches in their rigging. More likely than not, both boats end in a tangled mass of fiberglass and Mylar as the crowd looks away in horror. If you’re lucky enough not to crash off-world, you frequently need to stop, take a deep breath, and rez a new boat.

Well, sports fans, it looks like those days of sailing carnage may be a thing of the past with H4! This morning Vin and I repeatedly collided a Larinda Lite and a Full Tradewind into each other. We never “fused” or crashed. The usual result was a moderate “bounce.”

If you look at the sequence of images to the right, you’ll see an example. In A-B, both boats are asail, and Vin’s Larinda Lite collides with my Tradewind. As you can see in C-D, Vin’s boat just bounces off. In this case, Vin was thrown well over 100m, which seems pretty extreme. However, in all other attempts today, the bounce was much smaller and seemed fairly reasonable.

It’s worth noting that in all our collision attempts the Larinda bounced while the Tradewind was minimally affected; every time the Tradewind hit the Larinda head-on, the Larinda was pushed back. This may be due to a ‘mass effect,’ since the full-sized Tradewind is far more prim-heavy than the Larinda Lite.

The pictures below show another example of the collision effect under H4. In ‘A,’ Vin’s Larinda hits the Tradewind’s port bow at an angle. ‘B‘ shows that the two boats very briefly overlap, and then the Larinda ‘bounces back’ a small amount (‘C’). The extra space gives both boats enough room to slide past each other safely (‘D’).

Head on collision test

A similar bounce takes place when boats hit the End Of the World (EOW). The magnitude of that bounce appears equivalent to what occurred in H1. However, as they always say in science journals, “more research is indicated.

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