Porting MS-DOS Graphics Applications

Are you hesitant about porting your favorite VGA MS-DOS program to Linux? Using this tutorial and SVGALIB, porting will truly become a matter of minutes.
Waiting for the VGA Retrace

By waiting for the VGA retrace, we are telling the program to wait until the monitor's electron beam reaches the bottom of the screen. Since there is a short pause before it jumps back to the top, it is a good moment to switch palettes without seeing “rainbow colors”. Thus, before switching palettes, we should wait for the VGA retrace as follows:

        while (!(inportb(0x3da) & 8));
        while ( (inportb(0x3da) & 8));
Setting the VGA Palette

The following code assumes you have a character array of 768 values, representing the RGB values for 256 colors. For example:

char palette[768];
        where palette[0] = R value of color 0;
        where palette[1] = G value of color 0;
        where palette[2] = B value of color 0;
        for (i = 0; i < 256; i++)
        vga_setpalette(i, palette[i*3],
                palette[i*3+1], palette[i*3+2]);
        for (i = 0; i < 768; i ++)
                outportb(0x3C9, palette[i]);

After adding SVGALIB code to the program, it's time to compile. Simply compile with the -lvga option to link the SVGALIB library. This library is preinstalled on most Linux systems; thus, if you experience problems linking it, you probably don't have it installed and should download it.

jaw3d was programmed by the author and is a Nullsoft Inc. product. Other cross-platform applications may be obtained at http://www.nullsoft.com/.


Jawed Karim is a freshman computer science student at the University of Illinois at Urbana-Champaign and works part-time at the National Center for Supercomputing Applications. His hobbies include programming and bicycle road racing. He can be reached at jkarim@students.uiuc.edu.


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