From: gpt20 AT thor DOT cam DOT ac DOT uk (G.P. Tootell)
Newsgroups: comp.os.msdos.djgpp
Subject: boo hoo i can't make this work :( (vesa stuff)
Date: 21 Nov 1996 18:50:45 GMT
Organization: University of Cambridge, England
Lines: 64
Sender: gpt20 AT hammer DOT thor DOT cam DOT ac DOT uk (G.P. Tootell)
Message-ID: <5728a5$sgq@lyra.csx.cam.ac.uk>
NNTP-Posting-Host: hammer.thor.cam.ac.uk
Keywords: vesa
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

ok, i read chapter 18 of the faq, i downloaded tutorials and stuff, i compiled
them, i understood most of em even :) *but* i'm stuck with this...

i'm trying to get the info about modes supported by a video card, now under real
mode there was no problem, i just followed the pointer, but despite various
(sometimes random) attempts at getting this to work under djgpp i can't do it :(
could someone please just tell me where i've gone wrong.
(the code should return the first supported screen mode into 'value', eventually
i want to return all the supported screen modes and find one that matches the
specs i supply.)

thanks muchly,
nik

ps. yes i know the seg and off calculations are really screwy, this is like the
454365436th rewrite of this code and i was clutching at straws by this time :)
it is true to say the pointer returned can be cast as a long in this way tho
right? at least under standard dos it was.. and the calculation for farpeek i got
from chapter 18 of the faq :(

#define PACKED __attribute__ ((packed))

#pragma pack(1)
/* SuperVGA information block */
typedef struct {
  char    VESASignature[4] PACKED;      /* 'VESA' 4 byte signature          */
  short   VESAVersion PACKED;           /* VBE version number               */
  char    *OEMStringPtr PACKED;         /* Pointer to OEM string            */
  long    Capabilities PACKED;          /* Capabilities of video card       */
  short   *VideoModePtr PACKED;         /* Pointer to supported modes       */
  short   TotalMemory PACKED;           /* Number of 64kb memory blocks     */
  char    reserved[236] PACKED;         /* Pad to 256 byte block size       */
} VBE_VgaInfo;
#pragma pack()

void VBE_detect(VBE_VgaInfo *vbeinfo) {
  	__dpmi_regs regs;
  	short value,seg,off;  

  	assert(sizeof(*vbeinfo)<_go32_info_block.size_of_transfer_buffer);
  	regs.x.ax=0x4F00;
  	regs.x.di=__tb & 0x0F;
  	regs.x.es=(__tb>>4) & 0xFFFF;
  	dosmemput(vbeinfo,sizeof(*vbeinfo),__tb);
  	__dpmi_int(0x10, &regs);
  	dosmemget(__tb,sizeof(*vbeinfo),vbeinfo);
  	if (strncmp(vbeinfo->VESASignature,"VESA",4)!=0) {
  		printf("vesa not supported.\n");
  		exit(0);
  	}
  	else {
  		seg=(unsigned long)vbeinfo->VideoModePtr>>16;
  		off=(unsigned long)vbeinfo->VideoModePtr & 0xffff;
  	        value=_farpeekw(_dos_ds,seg*16+off);
		printf("%d ",value);
	}
}





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