Sender: nate AT cartsys DOT com
Message-ID: <377D4C68.16AD5C62@cartsys.com>
Date: Fri, 02 Jul 1999 16:34:00 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
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To: djgpp AT delorie DOT com
Subject: Re: Virtual Screens
References: <7lgctl$7r4$1 AT news5 DOT svr DOT pol DOT co DOT uk> <930893939 DOT 241152 AT kyle DOT inet DOT net DOT nz>
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Reply-To: djgpp AT delorie DOT com

David Mitchell wrote:
> 
> This is how I do it.
> Note: This code can be very much optimised! And the putPixel method is
> missing the clipping code.

I suggest that flipping be done as:

dosmemput(vscreen, 0xa0000, 64000);

instead.  It's much safer and all of maybe 3 cycles slower (and
nearptr_enable is an expensive DPMI call itself, although it isn't in
the inner loop).

If you insist on using the nearptr hack, then for the sake of your
sanity use __djgpp_nearptr_disable whenever you can.

> 
> char vscreen[64000];
> char *scrptr;
> 
> void putPixel(int x, int y, char color) {
>     int offs;
> 
>     offs = 320*y + x;
> 
>     vscreen[offs] = color;
> }
> 
> void flip(void) {
>     memcpy(scrptr, virt, 64000);            // #include <mem.h>
> }
> 
> int main(void) {
>     .
>     .
>     .
>     __djgpp_nearptr_enable();                    // #include <sys/nearptr.h>
> for this.
>     scrptr = (char*) (__djgpp_conventional_base + 0xa0000);    // note 4
> zeros because of
> 
> // pmode
>     .
>     .
>     .
> }
> 
> David.
> 
> PS the flip takes less than 1ms on a P200

-- 

Nate Eldredge
nate AT cartsys DOT com