Date   : Mon, 04 Feb 2002 23:45:18 GMT
From   : Thomas Harte <thomasharte@...>
Subject: Re[1]: Firetrack

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> I haven't entirely worked out how to do this, because it 
involves rewriting
> a lot of code, and using the total height generated by the 
previous frame as
> a guide to where the current frame starts, e.g. if frame 2 
generates 264
> lines, then frame 3 must have line 132 as dead centre. 
Either that or doing
> some devious data re-arrangement at time of writing the 
screen data to the
> PC screen.

You don't need to do all that! Just keep track of the various 
counters each scanline and only enter VSYNC (and HSYNC if 
you want a really accurate emulation) and hence adjust which 
PC line you are writing to in that manner when the correct 
counters do the correct thing. What I mean is, why take an 
overview and start worrying about how many total scanlines 
were drawn each frame when the CRTC doesn't?

There used to be a particularly good document about it at the 
Unofficial Amstrad WWW Resource, but it seems to be gone 
nowadays. I may still have a copy though - I'll have a look and 
post a summary if I can find it.

-Thomas
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