[Coco] 8 color coco 2 graphic display

[Luis Antoniosi (CoCoDemus)]

Sock Master said on his webpage he has patched it for Coco3 but I don't see
any binary available.


On Mon, Apr 22, 2013 at 5:46 AM, Fedor Steeman <petrander at gmail.com> wrote:

> Sounds like some pretty awesome trickery, Torsten. I wish more game
> programmer's did these at the time. Unfortunate that the CoCo3 doesn't
> support it. What could be the reason? Also, I wonder if the CoCo FPGA /
> CoCo-X supports it?
>
> BTW if anyone happens to have some source code to demonstrate this trick
> that would be really nice!
>
> > Try the latest version of XROAR, should do the trick for both NTSC and
> PAL
> > emulation.
>
> Are you saying that XROAR shows Dragonfire displayed as intended?? That
> sounds really cool. I'd better download that and dust up my .rom files.
>
> Anyone happen to have the Dragonfire game as bin or virtual disk?
>
> Cheers,
> Fedor
>
>
>
> On 21 April 2013 14:47, Torsten Dittel <OS-9 at trs-80.cc> wrote:
>
> > Ben <ben_jimenez at ...> writes:
> >
> > > Is there some sample code around on how to do this?
> >
> > Hi Ben, here's what I remember after 30 years:
> >
> > The trick is switching graphics modes (e.g. Dragonfire: BASICally spoken
> > switching between SCREEN1,0 and SCREEN1,1 of PMODE3,1) during the screen
> > image is generated line by line by the VDG.
> >
> > This has to be at least be synchronized with the vertical blank (VSYNC,
> > every 16.67ms on NTSC, every 20ms on PAL machines), either by polling the
> > corresponding PIA bits or by implementing a corresponding interrupt
> service
> > (on IRQ).
> >
> > You could then manually count CPU cycles of the code you're executing in
> > the mean time, to know where you are on the screen (switching can be done
> > as well in the middle of a line, even several times as Dragonfire proves)
> > to make sure the switching always takes place at the same point of time
> > (and thus point on the screen) after the vertical blank occured, but this
> > requires to create symmetrical code if you have conditional branches.
> >
> > Or you could waste all the CPU cycles by staying in a loop until the
> > switching point is reached.
> >
> > Or you could additionally setup a Fast HSYNC (FIRQ) interrupt service
> > routine which counts the scan lines (should be reste by the VSYNC then)
> and
> > triggers the switching at a certain scan line. For the "fine tuning" of
> the
> > horizontal position of the mode change, you would then use opcodes
> > like "NOP" (2~) or "BRN" (3~), if there's nothing senseful else to do for
> > the interrupt service routine.
> >
> > It depends on what else you want to do during the "mixed mode" is
> > displayed. Each approach has it's advantages and disadvantages. So I
> assume
> > to provide code examples one would need to understand what you're
> planning
> > to do.
> >
> > > Of course the trick didn't work in the vcc emulator, but I'd like to
> try
> > > and do this on my real coco 2.
> >
> > Try the latest version of XROAR, should do the trick for both NTSC and
> PAL
> > emulation.
> >
> > Regards, Torsten
> >
> >
> > --
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> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
> >
>
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>



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