Hello World!
I'm talking about collisions in Alice3.
I'm continuing with the movie with the fish that we 
added default model manipulation to.

When we run the movie the user can drag the fish and reposition them.
Right now, nothing happens when the fish collide with each other.
I would like to make it so that if one of these fish
collides with the blue tang, the blue tang says, "Watch where you're going!"

I'm going to add an event listener for when a collision starts.
There are two arguments, both of them are arrays.
The first array are the items that get bumped into.
And the second array are the objects that caused the bumping,
the ones that were moving.
I'm going to put all three fish in each of those two arrays.

Then we are going to use an if
and change that to compare two SThings.
I'm going to make the first one the blue tang
and the second one the blue tang.

Then I'm going to drag this function that tells me if the blue tang
is in the set of things that got bumped into.
When that happens, the blue tang is going to say, "Watch where you're going!"
Let's run that and see what happens.
If we move the blue tang nothing happens when he collides with the other fish.
But if I move one of the other fish
and they caused the collision the blue tang says, "Watch where you're going!"

If I wanted the blue tang to say, "Oh, excuse me!"
(Let's copy this to the clipboard and drag it down here.)
If the blue tang is the one that did the collision, set B,
Blue tang is going to say, "Excuse me."

Let's run that.
So if the blue tang is moving and he bangs into another fish
he says "Excuse me."
If the other fish move into him he says "Watch where you're going."
That's it!
You can see the whole code here.