Manual pages › X Window and screen libraries (3X)

XSeStandC(3X)

set or get standard colormaps

From the original Amiga UNIX 2.1 manual. Some things it mentions may not be in this release.

NAME

XSetStandardColormap, XGetStandardColormap - set or get standard colormaps

SYNTAX

XSetStandardColormap(display, w, colormap, property)
      Display *display;
      Window w;
      XStandardColormap *colormap;
      Atom property;     /* RGB_BEST_MAP, etc. */

Status XGetStandardColormap(display, w, colormap_return,
property)
      Display *display;
      Window w;
      XStandardColormap *colormap_return;
      Atom property;     /* RGB_BEST_MAP, etc. */

ARGUMENTS

colormap  Specifies the colormap.

colormap_return

Returns the colormap associated with the specified atom.

display   Specifies the connection to the XWIN server.

property  Specifies the property name.

w         Specifies the window.

DESCRIPTION

The XSetStandardColormap function usually is only used by
window managers. To create a standard colormap, follow this
procedure:

1. Open a new connection to the same server.

2. Grab the server.

3. See if the property is on the property list of the root window for the screen.

4. If the desired property is not present:

•    Create a colormap (not required for

     RGB_DEFAULT_MAP)

•    Determine the color capabilities of the display.

•    Call XAllocColorPlanes or XAllocColorCells to

allocate cells in the colormap.

XWIN 3.0               Last change: 9/1/88                 .ie t

          •    Call XStoreColors to store appropriate color

values in the colormap.

• Fill in the descriptive members in the XStandard-Colormap structure.

• Attach the property to the root window.

     •    Use XSetCloseDownMode to make the resource per-
          manent.

5.   Ungrab the server.

XSetStandardColormap can generate BadAlloc, BadAtom, and
BadWindow errors.

The XGetStandardColormap function returns the colormap
definition associated with the atom supplied as the property
argument.  For example, to fetch the standard GrayScale
colormap for a display, you use XGetStandardColormap with
the following syntax:

XGetStandardColormap(dpy, DefaultRootWindow(dpy), &cmap, XA_RGB_GRAY_MAP);

Once you have fetched a standard colormap, you can use it to convert RGB values into pixel values. For example, given an XStandardColormap structure and floating-point RGB coefficients in the range 0.0 to 1.0, you can compose pixel values with the following C expression:

pixel = base_pixel
     + ((unsigned long) (0.5 + r * red_max)) * red_mult
     + ((unsigned long) (0.5 + g * green_max)) * green_mult
     + ((unsigned long) (0.5 + b * blue_max)) * blue_mult;

The use of addition rather than logical OR for composing
pixel values permits allocations where the RGB value is not
aligned to bit boundaries.

XGetStandardColormap can generate BadAtom and BadWindow
errors.

DIAGNOSTICS

BadAlloc  The server failed to allocate the requested

resource or server memory.

BadAtom   A value for an Atom argument does not name a

defined Atom.

BadWindow A value for a Window argument does not name a

defined Window.