XSetStandardColormap(3X11)

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

colormapSpecifies the colormap.

colormap_return
Returns the colormap associated with the specified atom.

displaySpecifies the connection to the X server.

propertySpecifies the property name.

wSpecifies 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.

•Call XStoreColors to store appropriate color values in the colormap.

•Fill in the descriptive members in the XStandardColormap structure.

•Attach the property to the root window.

•Use XSetCloseDownMode to make the resource permanent.

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.