Mail Archives: djgpp/1997/10/21/03:01:32
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I think I saw allegro doing such things - people told me it's quite
useful.
Genady
Nate Eldredge wrote:
>
> At 12:16 10/17/1997 GMT, waage wrote:
> >I am having problems copying info from a virtual screen allocated with
> >malloc and copying it to the VGA 0xa000. The code looks like this,
> >when compiled it says no errors but when I try to write to the virtual
> >screen with my put_pixel it crashes.
> >
> >This is the function that allocates the virtual screen and (I hope)
> >returns the address in memory where its located.
> >
> >unsigned long set_virtual(int w, int h) {
> > unsigned long v_size = w * h;
> > unsigned long vir_scr;
> > (void *)vir_scr = malloc(v_size);
> >
> > if(vir_scr != NULL) {
> > printf("Allocated memory for virtual screen.\n");
> > return vir_scr;
> > }
> > else {
> > printf("Unable to allocate %U bytes for virtual screen.\n",
> >v_size);
> > return 0;
> > }
> >}
> >
> >This is my put_pixel function, where is the address in memory that it
> >wants to write to.
> >
> >void put_pixel(int where, int x, int y, unsigned char *col) {
> > _farpokeb(_dos_ds, where*16+(x+(y*320)), col);
> > }
> >
> >This does not work with the virtual screen. Can anyone tell me if it
> >is because the virtual screen has a different selector than the a000
> >(the info said that _dos_de has a limit of 1MB)? Does malloc(...) use
> >memory above 1mb and do I need to use a different selector? I thought
> >of this and came up with this:
> That's it exactly. All your program's code and data is addressed relative to
> the _my_ds() selector. You don't need to use farptr functions to access it.
> >
> >short get_virtual_discriptor(unsigned long vir_scr) {
> > return(__dpmi_segment_to_descriptor(vir_scr));
> > }
> >
> >void put_vir_pixel(short sel, unsigned long where, int x, int y,
> >unsigned char col) {
> > _farpokeb(sel, where*16+(x+(y*320)), col);
> > }
> Do this to put_pixel your vir_scr:
> *(unsigned char *)vir_scr+x+(y*32) = col;
>
> Nate Eldredge
> eldredge AT ap DOT net
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