X Version 11 (1 September 1988) XSetStandardColormap(XS)
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 X 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.
⊕ 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.
SEE ALSO
Xlib - C Language X Interface
(printed 2/12/90) (1 September 1988)XSetStandardColormap(XS)