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Collision Detection and Resolution in Luxe

Posted on 2016-07-29

Tagged with: Luxe

Disclaimer: I just started using Luxe. First impression: engine seems very usable (great API design) and things work well. But, very poorly documented (API docs are sparse and there aren't many blog posts about how to do things using Luxe.)

I'm working on a small arena 2D shooter in Luxe. I have a ship (Sprite instance) and a bunch of walls (also Sprite instances). How can I:

• Find out when the ship hits a wall?
• Prevent the ship from moving into the wall, or move the ship back out of the wall after the collision?

Luxe includes a number of packages/classes related to collision detection. I stumbled upon the Polygon class. It includes two helpful methods:

• Polygon.rectangle(x, y, width, height): create a rectangular polygon, specifying position and size.
• polygonInstance.testPolygon(polygon): check if polygonInstance intersects testPolygon.

if testPolygon finds an intersection, it returns a non-null object with a number of fields. Of interest to us is the separation property, which tells us how much to move polygonInstance to get it to stop colliding with polygon.

Putting these together, we get something like this:

var shipPolygon = Polygon.rectangle(ship.pos.x, ship.pos.y, ship.size.x, ship.size.y);
var wallPolygon = Polygon.rectangle(wall.pos.x, wall.pos.y, wall.size.x, wall.size.y);
var result = shipPolygon.testPolygon(wall);
if (result != null)
{
    ship.pos.x += result.separation.x;
    ship.pos.y += result.separation.y;
}

This correctly causes the ship to stop when it hits wall.