Conference hydra::amiga_v1

1037.0. "sprites" by MEO78B::MCGHIE (looking for a door...) Tue Jan 05 1988 20:44

    Hi,
    
    anyone tried using AmigaBASIC for any 'object' graphics programming.
    At the moment it's the only language I've got so I'm playing around
    animating sprites etc.
    
    I have had a few problems. One is collision detection. I created
    an object with the object editor (supplied on the EXTRAS disk) and
    tried animating it. I used the example shown with the object.shape
    statement in the basic manual. So it was supposed to rebound from
    the edges. This it did most of the time, but every once in a while
    the object seemed to get 'stuck' between the border and something
    else.
    
    After experimenting, the conclusion I came to was that the collision
    detection routines were in fact detecting a second collision with
    the same border. This caused my collision handler to reverse
    the object direction again causing it to plow back into the edge.
    So setting up an oscillating state.
    
    I got around it with two different mechanisms.
    
    The first was once collision was detected, I moved the object away
    from the offending border by changing the relavant X or Y coordinate.
    This seemed to work quite well and if the size of the shift small
    enough, it was not apparent to the eye.
    
    The second method was to check to see what direction the object
    was moving in when the collision was detected.
    
    For example:
    	 if the object was moving to the left (i.e. negative x velocity)
    	and the collision detected was with the left border then I would
    	reverse the x velocity causing the object to rebound.
    	However if the velocity was positive (moving to the right) and
    	the collision was with the left border then I do not reverse
	the velocity.

    
    Am I doing something wrong, or is there bugs in the collision detection
    part of the Amiga or maybe BASIC.
    
    Have other people had problems with collision detection in other
    languages.
    
    
	regards
    		Mike
    		(Melbourne, in the Land Downunder)
    

    I don't have any solutions for you, but can confirm your sanity
    by saying I've had the same problems and discovered pretty much
    the same solutions.  As you have probably also discovered, even
    though BASIC tries to make the interfaces to sprites and bobs
    identical, they have different bugs.  It's easier to get around
    the bugs in sprites - change direction based on wall hit and not
    just previous direction.  Bobs tend to leave small smears on the
    screen.  I haven't found a way to avoid them yet.
    
    The animation in BASIC was a good idea, and seems to be well designed
    from a user interface point of view, but I have pretty much given
    up on it for even semi-serious work.
    
    Good luck.