XSetStandardColormap(3X11) BSD 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
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