Re: Hires calculations

[Charles Stephens <devnull@dobbs.eng.sun.com>]

>>>>> "BR" == bobryan9  <bobryan9@my-dejanews.com> writes:

 BR> How do I calculate the MEMORY LOCATION of a byte on the LEFT SIDE
 BR> of the Hires screen, given the Y location?

 BR> I would like something like:

 BR> MEMLOC=Y (insert math here)

To find a memory location for a given hi-res coordinate, use this
handy formula (remember everything is integer math):

location = base+(40 * cluster)+(128 * clusteroffset)+(1024 * line) + pixelgroup

base = 8192 (for page 1) or 16384 (for page 2)
pixelgroup = x / 7
row = y / 8
line = y mod 8
clusteroffset = row mod 8
cluster = row / 8 

Example, you want to find the address for 100,75 on Hi-Res page 1:

base = 8192
pixelgroup = 14
row = 9
line = 3
clusteroffset = 1
cluster = 1

Now, plug it all in:

location = 8192 + (40 * 1) + (128 * 1) + (1024 * 3) + 14
location = 11446 or $2CB6

cfs
-- 
Charles F. Stephens               = "I don't like the cores,
Software Psychic and Illuminary   =  but the cores like me!"
Solaris Directory Service         =            -- Marilyn Manson, paraphrased
Solaris Software                  = "We don't make mistakes, we make
Sun Microsystems, Inc.            =  happy accidents."
Menlo Park, California, USA       =            -- Bob Ross