From: "Michael Stewart" <mike AT reggin DOT freeserve DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problems with video class in C++
Date: Tue, 2 Mar 1999 18:35:58 -0000
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Dylan Trotter wrote in message <36d1f59d DOT 0 AT nemo DOT idirect DOT com>...
>Hi


Hello

>/*This is the assignment for the screen pointer which should point to the
>VGA segment*/
>screen = (unsigned char *) 0xA0000 + __djgpp_conventional_base;


Fine


>/*This dynamically allocates memory for the 320x200x8 buffer*/
>buffer = new unsigned char[64000];
>
>/*This is the put_pixel routine I am using*/
>inline void video::put_pixel(int x, int y, unsigned char col)
>{
> if (col != trans_col[0])
> {
>  if (x < 0) x = x_resolution + (x % x_resolution);
>  if (x >= x_resolution) x %= x_resolution;
>  if (y < 0) y = y_resolution + (y % y_resolution);
>  if (y >= y_resolution) y %= y_resolution;
>
>  buffer[y * bytes_per_scanline + x] = col;
> }
>}


Surely this would be a little better.

void video::put_pixel (int x, int y, unsigned char col) {
   if (col != trans_col[0]) return;

   if (x < 0 || x >= x_resolution) return; // No point displaying a pixel
that is out of bounds
   if (y < 0 || y >= y_resolution) return;

   buffer[y * bytes_per_scanline + x] = col; // Don't forget this will only
work like this in 8 bit modes.
}

>/*And this is the routine to copy the buffer to the screen*/
>inline void video::show_buffer()
>{
> wait_for_vertical_retrace();
>
> for(int y = 0; y < y_resolution; y++)
>  memcpy((unsigned char *) (screen + (y * bytes_per_scanline *
>bytes_per_pixel)),
>                  (unsigned char *) (buffer + (y * x_resolution *
>bytes_per_pixel)),
>                  x_resolution * bytes_per_pixel);
>}


Don't see any problem here. But I think for a bit more speed you might want
to set the buffer to the same size as the screen. That way you could just
use, this would cut out all the looping.
memcpy (screen, buffer, screen_size);

>Another quick question I have is whether there is a software interrupt I
>could call to return the current video mode (preferably including extended
>SVGA modes).


Yup, from the VESA spec

        Input:  AH = 4Fh        Super VGA support
                AL = 02h        Set Super VGA video mode
                BX = Video mode
                     D0-D14 = Video mode
                     D15 = Clear memory flag
                           0 = Clear video memory
                           1 = Don't clear video memory

        Output: AX = Status
                (All other registers are preserved)

The interrupt you need is 0x10. You had better get hold of the VESA spec
(www.vesa.org) as there are alot of other functions that you should look at.

>video::~video()
>{
> if (buffer != NULL) delete [] buffer;
>}


Can't see a problem here.



--
Michael Stewart
mike AT reggin DOT freeserve DOT co DOT uk
"Just because you're paraniod doesn't mean they aren't after you..."