Re: Apple Computer, Inc made mistake to do SHR?

[Michael Kent <n.kent@webtv.remove.this.com>]

Immortal Nephi <Immortal_Nephi@hotmail.com> wrote:

> Super High Resolution on Apple IIgs is supposed to have 256 colors on
> 320x200 resolution for any games.  Only 16 colors can be used each
> horizontal line on any games.  Do you have idea why Apple Computer,
> Inc decided to design and limit 16 colors?  I wonder Apple IIgs do
> have enough memory to hold 256 possible colors each pixel instead of
> each horizontal line.  Please advise.

Enough physical memory?  Yes.  Enough video memory?  No.  The Super Hi-Res
(SHR) modes of the Apple IIgs are designed to use 32K of video memory.
32K / (320x200) or (640x200) yields 4 bits / pixel in 320 mode or
2 bits / pixel in 640 mode.  That equals 16 colors / pixel in 320 mode or
4 colors / pixel in 640 mode.  Apple used the extra 768 bytes left over to
increase the palette from 16 to 4096 through a fairly complicated means.

Not elegant, but it worked.  The Apple II has never been known for its
elegant video modes.  :)

Mike

-- 
Michael Kent                                             Apple II Forever!
St. Peters, MO
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