Re: Blech! How can you stand 640x200??

[mister_boffo@hotmail.com (Mr. Boffo)]

On Sun, 24 Dec 2000 22:22:09 +1300, dempson@actrix.gen.nz (David
Empson) wrote:

>Mr. Boffo <mister_boffo@hotmail.com> wrote:
>
>> So anyway I've been trying out stuff like Hyperstudio for the IIgs,
>> and the one thing which keeps coming to mind is: "Boy, this screen is
>> just godawful!"
>> 
>> What exactly was the point of limiting the IIgs to a maximum of
>> 640x200?
>
>The screen resolution of every Apple II is designed to be compatible
>with standard television, but without interlace (which would cause
>flicker).
>
>This sets the horizontal scan frequency (about 15.75 kHz), refresh rate
>(50 or 60 Hz depending on locality) and hence the number of lines of
>vertical resolution (192 or 200, depending on video mode).
>
>To get a higher vertical resolution requires either
>
>(a) Interlacing the image at half the scan rate.  This would produce
>excessive flicker on a computer monitor.

Ah, yes, I recall seeing this on an Amiga, where the screen was an
NTSC monitor and the resolution required 60hz interlacing. A single
horizontal line has terrible flicker, unless made to be two lines
thick, so there's no real gain from the extra resolution. (sigh)

>The same video chip can support interlaced video (640x400) by using two
>32KB buffers in adjacent banks (which means that the video memory is no
>longer linear), but this is only supported on Apple's Video Overlay
>Card, not in the IIgs implementation.

Hee, it's an Apple product, so who cares about bank linearity? Anyone
who has ever dealt with the hell that is double-high and double-low
res graphics knows that Apple is no stranger to bizarre video bank
arrangements. :-)

-Mr. Bofo

Email: mister_boffo@hotmail.com