Date: Mon, 26 Sep 1994 16:35:15 +22305931 (WAUST)
From: Ron Grunwald <rgrunwal AT bluering DOT cowan DOT edu DOT au>
Sender: Ron Grunwald <rgrunwal AT bluering DOT cowan DOT edu DOT au>
Reply-To: Ron Grunwald <rgrunwal AT bluering DOT cowan DOT edu DOT au>
Subject: Re: Simple Graphics w/ DPMI?
To: djgpp AT sun DOT soe DOT clarkson DOT edu

Hi all again,  


Since my last posting describing how pixel graphics could be implemented
under DPMI and successfully work in a full screen DOS box under Windows,
a number of people have requested how it could be done, and also whether
I could provide some sample source code.

Well, here are portions of the code that I'm currently using. I should
apologize for the lack of documentation in these sources. I do intend
to work on this soon however.


Hope this helps for people intending to do similar type of programming.




Regards, Ron.


-------------------------------------------------------------------------------
  .
  .
  .

  #ifdef USE_DPMI_INTERFACE

     Descriptor_object.Create_LDT_Descriptor_DPMI(
                Display_segment_descriptor.base_pointer_32,
                Display_segment_descriptor.segment_limit_20);

     if(Descriptor_object.Get_Errorstate()) {
        printf("DGLSOLID Fatal  : Unable to create screen segment descriptor!\n");
        exit(FATAL_ALLOC_DESCRIPTOR);
     }

     Globl_display_segment_selector = Descriptor_object.GetSegmentSelector();
  #endif
-------------------------------------------------------------------------------

The definition for "Create_LDT_Descriptor_DPMI" follows below:


void GDT_DescriptorOperations_32Bit::Create_LDT_Descriptor_DPMI(
     Word32 segBaseAddr,
     Word32 segLimit) {

   classSegmentBaseAddress = segBaseAddr;
   classSegmentLimit       = segLimit;

   LDT_segmentSelector = DPMI_AllocateSingle_LDT_Descriptor();
   if(LDT_segmentSelector == NUMERIC_NULL) {
      Operation_Finalstate = FATAL_ALLOC_DESCRIPTOR;
      return;
   }

   Operation_Finalstate = DPMI_WriteBaseAddress_LDT_Segment(LDT_segmentSelector,
                                                            classSegmentBaseAddress);
   if(Operation_Finalstate) {
      Operation_Finalstate = ERROR_WRITE_BASEADDR;
      return;
   }

   Operation_Finalstate = DPMI_WriteLimit_LDT_Segment(LDT_segmentSelector,
                                                      classSegmentLimit);
   if(Operation_Finalstate) {
      Operation_Finalstate = ERROR_WRITE_LIMIT;
      return;
   }

   Operation_Finalstate = NON_ERROR;
}
-------------------------------------------------------------------------------

Below follow the definitions for:

i.    Creating an LDT descriptor under DPMI.
ii.   Writing a linear base address into the LDT descriptor.
iii.  Writing the segment limit into the descriptor.


Word16 GDT_DescriptorComponents_32Bit::DPMI_AllocateSingle_LDT_Descriptor(void) {

   registers_80x86.x.ax = 0x0000;
   registers_80x86.x.cx = 1;

   int86(0x31, &registers_80x86, &registers_80x86);

   if(registers_80x86.x.cflag)
      return(0x0000);
   return(registers_80x86.x.ax); // This is the selector that DPMI returns.
}


Byte GDT_DescriptorComponents_32Bit::DPMI_WriteBaseAddress_LDT_Segment(
     Word16  LDT_Selector,
     Word32  segmentBaseAddress) {

   registers_80x86.x.ax = 0x0007;
   registers_80x86.x.bx = LDT_Selector;
   registers_80x86.x.cx = (segmentBaseAddress >> 16) & 0x0000FFFF;
   registers_80x86.x.dx = segmentBaseAddress & 0x0000FFFF;

   int86(0x31, &registers_80x86, &registers_80x86);

   return((Byte)(registers_80x86.x.cflag));
}


Byte GDT_DescriptorComponents_32Bit::DPMI_WriteLimit_LDT_Segment(
     Word16  LDT_Selector,
     Word32  segmentLimit) {

   registers_80x86.x.ax = 0x0008;
   registers_80x86.x.bx = LDT_Selector;
   registers_80x86.x.cx = (segmentLimit >> 16) & 0x0000FFFF;
   registers_80x86.x.dx = segmentLimit & 0x0000FFFF;

   int86(0x31, &registers_80x86, &registers_80x86);

   return((Byte)(registers_80x86.x.cflag));
}
--------------------------------------------------------------------



 ********************************************************************
 | Author.............. Ron Grunwald                                | 
 | Internet............ rgrunwal AT bluering DOT cowan DOT edu DOT au              | 
 | Phone............... (09)273 8027 or (09)273 8468                |
 |------------------------------------------------------------------|
 | Department.......... Information Technology                      | 
 | Division/Faculty.... Operations and Systems Management           | 
 | Institute........... Edith Cowan University, Churchlands         | 
 | Location............ Perth, Western Australia                    |
 ********************************************************************
 "I don't have any solution but I certainly admire the problem!"