Collision detection.

[Anxiety]

How can i detect if two images are colliding?

I quess i dont have to say anything else anymore than thank you.

[ivan]

How can i detect if two images are colliding?

I quess i dont have to say anything else anymore than thank you.

There's 2 general approaches that I can think of at the moment.
1.Bitmasking
You create a bitmask for every image where each pixel is either 0 or 1 then you test the two bitmasks for overlapping pixels
As far as I know, this approach is pretty rare except for very specific games
2.Bounding volumes
You associate a bounding volume to each sprite (such as a circle or a rectangle) and test for a collision between the bounding volumes

[Robin]

How can i detect if two images are colliding?

Check whether the two rectangles that make up the images are intersecting. There is a very simple function for that, but I don't know it by heart, it's on this forum somewhere though.

[ivan]

Depends on your rect implementation.
The easiest version is when your rect is represented by a left, top, right and bottom value.
The code then becomes:

Code: Select all

--         -----------
-- -----------       |
-- |       | |(b2)   |
-- |  (b1) | |       |
-- |       -----------
-- -----------

-- Tests rect (b1) against rect (b2)
-- Returns true if they intersect
function RectVsRect ( r1l, r1t, r1r, r1b, r2l, r2t, r2r, r2b )
    if r1r < r2l or r1l > r2r then
        return false
    end
    if r1b < r2t or r1t > r2b then
        return false
    end
    return true
end

[kikito]

How can i detect if two images are colliding?

Check whether the two rectangles that make up the images are intersecting. There is a very simple function for that, but I don't know it by heart, it's on this forum somewhere though.

It's actually on the wiki: BoundingBox.lua. That's a bit simpler than ivan's implementation

[Lafolie]

I use this function that has been passed down from thread to thread many times apparently, ha. I don't know the original author.

Code: Select all

function overlap(x1,y1,w1,h1, x2,y2,w2,h2)
  return not (x1+w1 < x2  or x2+w2 < x1 or y1+h1 < y2 or y2+h2 < y1)
end

[Franc[e]sco]

I have a Rectangle class and I just do ptinrect of all the vertex of rect1 in rect2 and ptinrect of all the vertex of rect2 in rect1 I'm quite sure there are more efficient ways to do it though.

Code: Select all

function Rectangle:ptinrect(pt)
	return (pt.x >= self.lt.x and pt.x <= self.rt.x and pt.y >= self.lt.y and pt.y <= self.lb.y)
end

function Rectangle:intersect(rect)
	return (
		self:ptinrect(rect.lt) or
		self:ptinrect(rect.lb) or
		self:ptinrect(rect.rt) or
		self:ptinrect(rect.rb) or
		rect:ptinrect(self.lt) or
		rect:ptinrect(self.lb) or
		rect:ptinrect(self.rt) or
		rect:ptinrect(self.rb)
	)
end