ohhh, im very sorry, i overstepped your suggestion

but i didnt really get the clue. you have to explain it carefully.

- check for collision:

yes, thats the main problem. do you mean a precollision over bounding boxes ?

- normalize the speed vector

up to now i realize movement over an always normalized direction vector and a speed scalar

- backtrace trajectory

sure, but the question is, with which method ?

for tracing the collision point (and later calculating the gradient of the small surface) i only see the method of line intersection