Re: Floating Bus quirks

[Jonathan Schattke <wizwom@ripco.com>]

palfhawk@thegrid.net wrote:

> I suspect the real problem with emulating mid screen mode changes is
> that they rely on the refresh rate of the monitor.  I don't know what
> rate Apple monitors were refreshed, but I'm sure it was a fixed
> frequency and probably a lot slower than todays monitors (which
> refresh at many different frequencies).  To emulate this correctly,
> you'd need to very accurately emulate the refresh rate of the apple
> monitor and render the screen image in a buffer, and then copy that
> buffer to the real video memory during the real vertical retrace.
> This would probably be a lot easier to pull off under DOS than
> Windows.

Not really too difficult for the easy ones - where they try to switch
every screen full.  The difficult part is if you want to do the overlay
trick - switch between two pages on the vertical interlace gap.  This
produces a very smoothly half bright image of each thing, and that would
mean having a 50% persistence in the video logic (which would have to be
done as a first step - every 60th of a emulator second, the screen
memory would dim by half maximum, and pixels would then be "OR"ed with
the existing screen)


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