XAllocStandardColormXpVersion 11 (RelXAllocStandardColormap(3X11)
NAME
XAllocStandardColormap, XSetRGBColormaps, XGetRGBColormaps,
XStandardColormap - allocate, set, or read a standard
colormap structure
SYNTAX
XStandardColormap *XAllocStandardColormap()
void XSetRGBColormaps(display, w, std_colormap, count,
property)
Display *display;
Window w;
XStandardColormap *std_colormap;
int count;
Atom property;
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 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
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XAllocStandardColormXpVersion 11 (RelXAllocStandardColormap(3X11)
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:
o Create a colormap (unless you are using the
default colormap of the screen).
o Determine the color characteristics of the visual.
o Allocate cells in the colormap (or create it with
AllocAll).
o Call XStoreColors to store appropriate color
values in the colormap.
o Fill in the descriptive members in the
XStandardColormap structure.
o Attach the property to the root window.
o 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,
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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
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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
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
XAllocColor(3X11), XCreateColormap(3X11), XFree(3X11),
XSetCloseDownMode(3X11)
Xlib - C Language X Interface
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