How to check for each side of an object separately?

[NewbiePeta]

I'm a newbie, and I don't really know how to check collision for each side of an object separately. Yes, there is this function,

Code: Select all

function CheckCollision(x1,y1,w1,h1, x2,y2,w2,h2) 
	return x1 < x2+w2 and
         x2 < x1+w1 and
         y1 < y2+h2 and
         y2 < y1+h1 
end

but it detects the collision of objects in general.

[pgimeno]

That function only tells you that the two rectangles intersect. Generally, when two rectangles intersect, you can't tell which sides are colliding; you can only tell that their intersection is not empty, and only in some special cases can you determine that the intersection lies completely in one of the sides of one of the rectangles. To put it shortly, the problem of "which sides are colliding" is not well defined.

However, given a previous position, you can tell which side a moving rectangle touched first when moving from its previous to its new position. That's what bump.lua calculates. It's not an easy calculation to do, so I'd suggest you to use that library.

[dusoft]

Or use the built-in polygon / collision handling.

[pgimeno]

Or use the built-in polygon / collision handling.

That's a bad idea. The built-in polygon/collision handling means you need to convert the whole program to use love.physics, and that changes the approach of the code radically, meaning basically a rewrite. It may also bring with it some unexpected side effects of using love.physics. Often, custom simple physics are better than using love.physics, especially if all you need is AABB collisions.

[dusoft]

Yes, that's correct, polygons/physics are overkill for simple AABB. Bump is a good proxy lib for that if one does not need complex logic. Otherwise, love.physics gives an exact contact point, which is useful.