Overlaps at an offset.

How does overlap at an offset work?

I'm trying to simply make a NPC turn when he's close to a wall, but it doesn't seem to trigger every time. If the offset is increased to 10 it seems to work, but shouldn't it work with just 1?

http://dl.getdropbox.com/u/930918/Offset.cap

Of course there are other ways to do this, but i still would like to know exactly how it works.

It's identical to moving the object the given number of pixels along the X and Y axes, testing an ordinary overlap, then moving it back again.

So why doesn't it allways work? Is it because the plattform movement isn't testing every pixel and sometimes miss and then stopps before the next frame?

Think it depends how fast the object moves. If you just use +1 offset and your object moves more than 1 pixel per frame, then yes, you'll find yourself in a fix. Because by that time you are well within the wall already, as you turn around and check for offset, you are still inside.

To be safe, factor movement speed into offset value. Or just move the object just outside the wall before turning it. It looks like ramming into the wall, staggering and then turning around.

I'll just use the "wall to the left" and "wall to the right" conditions for this.