Re: A86: ASM Converter from 85->86


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Re: A86: ASM Converter from 85->86



On Sat, 2 Aug 1997, James Yopp wrote:

> Yeah.  I'm working on Asteroids.  My current problem is that when the 
> ship moves so that the back half of it is off the screen, the dx and dy 
> of the lines composing the ship get messed up. I'm using Stephanie 
> Jantzen's line routine, based on Bresenham's algorithm, to do this, 
> because it uses FindPixel for every pixel in the line, and that way I can 

Does anyone know anything about _ILine?  Does it call the system FindPixel
for every point on the line?  That seems inefficient, since all the points
in a line are right next to each other.  Does someone have Bresenham's
algorithm handy?  I've experimented with it in the past, but I'm not a CG
major, so such things easily leak out of my mind.

> to adjust the coordinates without affecting line direction. To fix the 
> problem, I'm going to have to move the viewable screen area to the middle 
> of the coordinate system so that the routine can accurately calculate the 
> distances. So, the screen system for the new game would go from (63, 127) 
> to (191, 63).  Anybody know of a better way to do this?

Have you thought about using signed comparisons?  Rather than using "jr
nc" and "jr c" you use "jr p" and "jr m".  Your 8-bit numbers range from
-128 to 127, which is just what you need for the LCD.

Have I answered your question?  I have a nagging feeling that I'm missing
something important.

--------
Dan Eble (mailto:eble@cis.ohio-state.edu)
         (http://www.cis.ohio-state.edu/~eble)



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