Re: Hires colors

[dalloff@freenet.columbus.oh.us (Dave Althoff)]

Philip Stephens (philip@labtam.OZ.AU) wrote:
: Fabrice Frances writes:

: >So, the resolution is 280 pixels, indeed. There's just proximity constraints.

:   Actually the resolution is 560 pixels, with proximity constraints!  The
: colour bit in each hi-res byte causes a half-pixel shift on the screen
: of all 7 pixels in that byte.  I remember a program published in Nibble
: magazine took advantage of this fact to draw lines and circles on the screen
: in a pseudo 560-pixel hi-res mode.  It was quite effective. 

Of course, to draw a horizontal 560-pixel line, you cut your vertical
resolution to 140 lines.  But because the dot-shift is only on individual
bytes, that is less of a problem than it might seem in the real world.

It's a bit like doing 3200 color images on a GS...it's another Dirty
Little Secret.  By the way, the text character set DOES use this feature. 
If you use, say, the hi-res character generator from the DOS Tool Kit,
which contains a font identical to the text character set, and activate
the double-hi-res screen, while you won't get 80-column text, you will get
text in every other column of an 80-column screen.  As a bonus, there is
no half-dot shift in double-hi-res.  There, you can see that certain
letters acquire a bad case of the jaggies.  The uppercase "A" comes to
mind off hand.  I'm real busy right now, but I'll post a program
(Applesoft) that demonstrates this more clearly.

(I won't bother with the other 560-hires demo I was going to write since
someone else already did that 8-})

 --Dave Althoff, Jr

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