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Tutorial - Palette
Author:Oren
Category:DOS Graphics
Uploaded at:28-May-03
Views:6669
The palette is used in 8-bit color depth (as used in mode13 for instance).

The palette is a buffer that contains definitions for 256 colors
(color = Red, Green, Blue).
The video buffer contains a Color Index for each pixel on the screen.
The color that would be displayed on the monitor is color number
'Color Index' from the palette.

That means that if a pixel's color index is 74, and color no. 74 in the
palette is RGB(63, 0, 0) (=Red) then that pixel will be red.

Each value in the palette (Red, Green or blue) should
be in the range of 0-63.
That means you have 64^3 = 262144 possible colors to display
(but remember - only 256 colors in the same time).

Playing with the palette you can make some cool effects
such as 'Fade In'/'Fade Out'.

You can set or retrieve each color from the palette pretty easily.

To set a color in the palette do:
void setpal(unsigned char col, 
            unsigned char r,
            unsigned char g,
            unsigned char b)
{
 outportb(0x3C8, col);
 // We send to port 0x3C8 the index of the color in the 
 // palette we want to change

 outportb(0x3C9, r);   // Send Red Value to port 0x3C9
 outportb(0x3C9, g);   // Send Green Value to port 0x3C9
 outportb(0x3C9, b);   // Send Blue Value to port 0x3C9
}

// The retrieve a color from the palette do:

void getpal(unsigned char col, 
            unsigned char *red, 
            unsigned char *green, 
            unsigned char *blue)
{
 outportb(0x3C7, col);
  // Send to port 0x3C7 the index of the color in the
  // palette we want to retrieve

 *red = inportb(0x3C9);   // Retrieve Red Value from port 0x3C9
 *green = inportb(0x3C9); // Retrieve Green Value from port 0x3C9
 *blue = inportb(0x3C9);  // Retrieve Blue  Value from port 0x3C9
}

Note: Palette may be found in other modes that use 8 bits per pixel

Source Code:
DJGPP - palette.c
Turbo C - palette.cpp

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