hello from italy; i have been looking around and i was not able to find a thread with this very simple problem. if there is one already please point me to it. i have an object that bounces of a wall, but i would like to set a mask_index on the wall so that the collision does not happen on the touching the first pixels. i have set up a mask_index on thw wall's sprite, but i simply don't understand how to code the bouncing object on using the mask_index instead of the full sprite. i tried: mask_index = spr_wall; but when when i check the content of mask_index it is always equal to 0. thanks, pietro.