XGetRGBColormaps()XGetRGBColormaps()NameXGetRGBColormaps – obtain the XStandardColormap structure associated
with the specified property.
Synopsis
Status XGetRGBColormaps(display, w, std_colormap_return, count_return,
property)
Display *display;
Window w;
XStandardColormap **std_colormap_return;
int *count_return;
Atom property;
Arguments
display Specifies a connection to an X server; returned from
XOpenDisplay().
w Specifies the window.
std_colormap_return
Returns the XStandardColormap structure.
count_return
Returns the number of colormaps.
property Specifies the property name.
Returns
Zero on failure, non-zero on success.
Availability
Release 4 and later.
DescriptionXGetRGBColormaps() returns the RGB colormap definitions stored in the
specified property on the named window. If the property exists, is of
type RGB_COLOR_MAP, is of format 32, and is long enough to contain a
colormap definition, XGetRGBColormaps() allocates and fills in space
for the returned colormaps, and returns a non-zero status. Otherwise,
none of the fields are set, and XGetRGBColormaps() returns a zero sta‐
tus. If the visualid field is not present, XGetRGBColormaps() assumes
the default visual for the screen on which the window is located; if
the killid field is not present, it is assumed to have a value of None,
which indicates that the resources cannot be released. Note that it is
the caller's responsibility to honor the ICCCM restriction that only
RGB_DEFAULT_MAP contain more than one definition.
XGetRGBColormaps() does not install the colormaps into the hardware
colormap, it does not allocate entries, and it does not even create
virtual colormaps. It just provides information about designs of col‐
ormap and the IDs of the colormaps if some other client has already
created them. The application can otherwise attempt to create a vir‐
tual colormap of the appropriate type, and allocate its entries accord‐
ing to the information in the XStandardColormap structure. Installing
the colormap must then be done with XInstallColormap(), in cooperation
with the window manager. Any of these steps could fail, and the appli‐
cation should be prepared.
If the server or another client has already created a standard colormap
of this type, then its ID will be returned in the colormap member of
the XStandardColormap structure. Some servers and window managers,
particular on high-performance workstations, will create some or all of
the standard colormaps so they can be quickly installed when needed by
applications.
An application should go through the standard colormap creation process
only if it needs the special qualities of the standard colormaps and if
another client has not already created them. For one, they allow the
application to convert RGB values into pixel values quickly because the
mapping is predictable. Given an XStandardColormap structure for an
XA_RGB_BEST_MAP colormap, 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 bound‐
aries.
XGetRGBColormaps() supersedes XGetStandardColormap().
For more information, see Volume One, Chapter 7, Color.
Structures
typedef struct {
Colormap colormap;
unsigned long red_max;
unsigned long red_mult;
unsigned long green_max;
unsigned long green_mult;
unsigned long blue_max;
unsigned long blue_mult;
unsigned long base_pixel;
VisualID visualid; /* added by ICCCM version 1 */
XID killid; /* added by ICCCM version 1 */
} XStandardColormap;
Errors
BadAtom
BadWindow
See AlsoXAllocStandardColormap(), XSetRGBColormaps().
Xlib - Window Manager Hints XGetRGBColormaps()
