From: ludvig <ludvig AT club-internet DOT fr>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Graphics:OK with 320x200 ->problem with higher resolution
Date: Fri, 19 Sep 1997 02:51:51 +0200
Organization: Grolier Interactive Europe
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abderahim DOT boukhairi AT hol DOT fr wrote:
> 
> I'm using since one month the compiler v2 . In the old version i got
> v1.1 it was easy to swap from 320x200 to 640x200 or to higher
> resolution .the location into memory was always the same 0xD000000.
>   //version 1 of compiler
>   /*memmove((char*)0xD0000000,back.virt,DEFX*DEFY);*/
> Writing to this location was always good and  not depending of the
> resolution.
> Since new version of the compiler i use
>   //version 2 of compiler
>    movedata(_my_ds(), back.virt ,_dos_ds, 0xA0000,DEFX*DEFY)
> 
> This is acting well when DEFX*DEFY = 320*200;
> but i always obtain segmentation violation when DEFX*DEFY = 640*480 or
> higher.
> it's perhaps that i have to write directly to graphic cards memory
> bank !
> Please tell me how to do that
> (my graphic card got 1 Mbyte of memory)
> thanks!
> email-me the answer to
> 
> abderahim DOT boukhairi AT hol DOT fr
Hi!

Do you use bankswitches?
I have never been using the D00000... adress I use the 'window' of 64kb
at A0000 with bank set to 0 to access the first 64kb of the screen
setting bank to 1 to write to the 64kb+1-128kb memoryspace on
screen(always writeing on A0000) and on.

the function to change banks:

int set_bank(int bank)
{
 __dpmi_regs reg;
 if(bank!=active_bank)
  {
	reg.h.ah=0x4f;
	reg.h.al=0x05;
	reg.h.bh=0x00;
	reg.h.dl=bank;
	reg.h.dh=0;
	__dpmi_int(0x10,&reg);
	active_bank=bank;
  }
 return(0);
}

BTW active_bank is a global variable(set to -1 in my init_graphics()
function) so that you don't need to waste time changing to the same bank
thats active and I think bank==0 when you switch on the graphic mode.

Hope it was this you needed.

Ludvig