Ubuntu Manpage: XAllocStandardColormap, XSetRGBColormaps, XGetRGBColormaps, XStandardColormap

NAME

       XAllocStandardColormap,  XSetRGBColormaps, XGetRGBColormaps, XStandardColormap - allocate,
       set, or read a standard colormap structure

SYNTAX

       XStandardColormap *XAllocStandardColormap(void);

       void XSetRGBColormaps(Display *display, Window  w,  XStandardColormap  *std_colormap,  int
              count, Atom property);

       Status      XGetRGBColormaps(Display     *display,     Window     w,     XStandardColormap
              **std_colormap_return, int *count_return, Atom property);

ARGUMENTS

       display   Specifies the connection to the X server.

       count     Specifies the number of colormaps.

       count_return
                 Returns the number of colormaps.

       property  Specifies the property name.

       std_colormap
                 Specifies the XStandardColormap structure to be used.

       std_colormap_return
                 Returns the XStandardColormap structure.

DESCRIPTION

       The XAllocStandardColormap function allocates and returns a pointer to a XStandardColormap
       structure.   Note  that all fields in the XStandardColormap structure are initially set to
       zero.  If insufficient memory is available, XAllocStandardColormap returns NULL.  To  free
       the memory allocated to this structure, use XFree.

       The  XSetRGBColormaps  function  replaces  the  RGB  colormap  definition in the specified
       property on the named window.  If the property does not  already  exist,  XSetRGBColormaps
       sets  the  RGB  colormap  definition  in  the specified property on the named window.  The
       property is stored with a type of RGB_COLOR_MAP and a format of 32.  Note that it  is  the
       caller's  responsibility  to honor the ICCCM restriction that only RGB_DEFAULT_MAP contain
       more than one definition.

       The XSetRGBColormaps function usually is only used by  window  or  session  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 (unless you are using the default colormap of the screen).

            •    Determine the color characteristics of the visual.

            •    Allocate cells in the colormap (or create it with AllocAll).

            •    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.

       XSetRGBColormaps can generate BadAlloc, BadAtom, and BadWindow errors.

       The XGetRGBColormaps function 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  nonzero  status.   If  the
       visualid  is  not  present,  XGetRGBColormaps assumes the default visual for the screen on
       which the window is located; if  the  killid  is  not  present,  None  is  assumed,  which
       indicates  that  the resources cannot be released.  Otherwise, none of the fields are set,
       and XGetRGBColormaps returns a zero status.  Note that it is the  caller's  responsibility
       to honor the ICCCM restriction that only RGB_DEFAULT_MAP contain more than one definition.

       XGetRGBColormaps can generate BadAtom and BadWindow errors.

STRUCTURES

The XStandardColormap structure contains:

/* Hints */

#define ReleaseByFreeingColormap ( (XID)
1L)
/* Values */
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;
XID killid;
} XStandardColormap;

The colormap member is the colormap created by the XCreateColormap function. The red_max,
green_max, and blue_max members give the maximum red, green, and blue values,
respectively. Each color coefficient ranges from zero to its max, inclusive. For
example, a common colormap allocation is 3/3/2 (3 planes for red, 3 planes for green, and
2 planes for blue). This colormap would have red_max = 7, green_max = 7, and blue_max =
3. An alternate allocation that uses only 216 colors is red_max = 5, green_max = 5, and
blue_max = 5.

The red_mult, green_mult, and blue_mult members give the scale factors used to compose a
full pixel value. (See the discussion of the base_pixel members for further information.)
For a 3/3/2 allocation, red_mult might be 32, green_mult might be 4, and blue_mult might
be 1. For a 6-colors-each allocation, red_mult might be 36, green_mult might be 6, and
blue_mult might be 1.

The base_pixel member gives the base pixel value used to compose a full pixel value.
Usually, the base_pixel is obtained from a call to the XAllocColorPlanes function. Given
integer red, green, and blue coefficients in their appropriate ranges, one then can
compute a corresponding pixel value by using the following expression:

(r * red_mult + g * green_mult + b * blue_mult + base_pixel) & 0xFFFFFFFF

For GrayScale colormaps, only the colormap, red_max, red_mult, and base_pixel members are
defined. The other members are ignored. To compute a GrayScale pixel value, use the
following expression:

(gray * red_mult + base_pixel) & 0xFFFFFFFF

Negative multipliers can be represented by converting the 2's complement representation of
the multiplier into an unsigned long and storing the result in the appropriate _mult
field. The step of masking by 0xFFFFFFFF effectively converts the resulting positive
multiplier into a negative one. The masking step will take place automatically on many
machine architectures, depending on the size of the integer type used to do the
computation,

The visualid member gives the ID number of the visual from which the colormap was created.
The killid member gives a resource ID that indicates whether the cells held by this
standard colormap are to be released by freeing the colormap ID or by calling the
XKillClient function on the indicated resource. (Note that this method is necessary for
allocating out of an existing colormap.)

The properties containing the XStandardColormap information have the type RGB_COLOR_MAP.

DIAGNOSTICS