I have a problem with the following code: float exp_collision_detection_y(GLfloat x_move, GLfloat y_move, GLfloat z_move, GLfloat x_stay ,GLfloat y_stay, GLfloat z_stay, GLfloat distance) { if (x_move>x_stay-distance && x_movey_stay-distance && y_movez_stay-distance) { y_move=y_stay-distance; } if (x_move>x_stay-distance && x_movey_stay+distance-0.04 && z_movez_stay-distance) { y_move=y_stay+distance; } return y_move; } It is the y-axis part of my collision detection. Here is an example: At the begining y_stay = 0 , z_stay = -4 , y_move = 2 , z_move = -4 and distance = 2 Now i increase z_move up to -2 but then i can''t make y_move < 2. (I thing with the code above this should be possible) But after increasing z_move > -2 , making y_move < 2 and then making z_move = -2 , i can set y_move and z_move at the values 2 and -4 (like at the begining) and then i can increase z_move up to -2 and make y_move < 2 . I think this is difficult to understand but i hope some one can help me!