Porting MS-DOS Graphics Applications

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));
        vga_waitretrace();

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]);
        outportb(0x3C8,0);
        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/.

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