Hi. I've just been thinking about collision handling in this vector-based game engine I'm trying to develop. All the objects are polygons with float-value vertices along with (x, y) coordinates for their "centres." I'm trying to see if I can develop "line-perfect" collision. What I do is before I actually move the objects in the game I use their velocities to calculate what the coordinates of their vertices will be. I create lines between these vertices for each object, as well as lines between the vertices and their correspondents in the original polygon (so, when you draw the lines, the objects look kind of 3D if they're moving fast enough). To test for collision, I check if any of these lines from two objects intersect at all. I made lines between the vertices of the "shadow" shape and the real shape in case a polygon is moving so fast it would be translated completely past another polygon when it's actually updated. Here's an image to help visualizing this: http://img197.echo.cx/img197/2035/collisiondiagram4tg.jpg What I want to do is if two objects will collide the update method would be altered for them so that they'd be just touching in the next frame, instead of overlapping. To keep the unit time on track I'd figure out what percentage of the unit time it would take the objects to move close enough to touch then figure out where they'd move in the remaining time based on whatever physics I use, which is what gets drawn to the screen.

I downloaded your tutorials oliii. They seem good though it might take me a while to wrap my head around the math. Thank you anyway.

I guess my real question is how do I determine the time (starting from time = 0) at which two moving polygons, either convex or concave, contact each other before overlapping.