---
name: "rgbpix"
section: "3g"
platform: "linux"
package: "libxg-dev"
version: "4.3-14"
release: "Debian 3.0 (Woody)"
platforms: ["linux"]
url: "https://new.carta.tech/rgbpix"
---

# rgbpix(3g)

## NAME

RGB, rgbpix, rdcolmap, wrcolmap

## SYNOPSIS

```

```

**#include \<libc.h\>** **#include \<libg.h\>**

**unsigned long	rgbpix(Bitmap \*b, RGB rgb)**

**void	rdcolmap(Bitmap \*b, RGB \*map)**

**void	wrcolmap(Bitmap \*b, RGB \*map)**

## DESCRIPTION

Colors are described by the red, green, and blue light intensities, in an **RGB** datum:

-

  ```
  typedef
  struct RGB {
  	unsigned long red;
  	unsigned long green;
  	unsigned long blue;
  } RGB;
  ```

Zero intensity means there is no component of the given color; hence, black is represented by zero in all three positions and white has the maximum unsigned long value in all three positions.

Some of the graphics functions, such as *point* (see [*bitblt*(3g)](/bitblt/3g.md)), take a *pixel value* argument, which is a single unsigned long. For a given bitmap, *rgbpix* returns the pixel value with a color closest to the color represented by the *rgb* argument.

There is a *colormap* associated with each Bitmap.  A colormap is an array of **RGB**s, of length 2^(2^*ldepth*), giving the colors for pixels 0, 1, 2, etc.

*Rdcolormap* reads the colormap for the given bitmap into the provided *map*, which must have enough space to hold it. *Wrcolormap* associates the given colormap with the given bitmap, if possible. (The hardware might not allow this.)

## CAVEAT

The X implementation of libg uses whatever colourmap is the default when it starts up. A call to *rgbpix* will result in a call to *XAllocColor* and the allocation of a new colour in the application's colourmap if there is room. If no new colours can be allocated *rgbpix* will return the closest pixel value approximating the requested colour. If an application calls *wrcolmap* the default colourmap is replaced with the new colourmap and from then on *rgbpix* will deal with the new colourmap.

## BUGS

These functions only work for the screen bitmap. This interface will have to be refined for screens with ldepth \> 3.

## SEE ALSO

[*graphics*(3g)](/graphics/3g.md), [*bitblt*(3g)](/bitblt/3g.md)