XAllocStandardColormap(XS) 6 January 1993 XAllocStandardColormap(XS)
X Version 11 (Release 5)
Name
XAllocStandardColormap - 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.
countreturn Returns the number of colormaps.
property Specifies the property name.
stdcolormap Specifies the XStandardColormap structure to be used.
stdcolormapreturn
Returns the XStandardColormap structure.
Description
The XAllocStandardColormap function allocates and returns a pointer to a
XStandardColormap structure. Note that all fields in the XStandardColor-
map structure are initially set to zero. If insufficient memory is
available, XAllocStandardColormap returns NULL. To free the memory allo-
cated 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
RGBCOLORMAP and a format of 32. Note that it is the caller's responsi-
bility to honor the ICCCM restriction that only RGBDEFAULTMAP 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 using the default colormap of the
screen).
+ Determine the color characteristics of the visual.
+ Call XAllocColorPlanes or XAllocColorCells to allocate cells in
the colormap.
+ Call XStoreColors to store appropriate color values in the color-
map.
+ Fill in the descriptive members in the XStandardColormap struc-
ture.
+ Attach the property to the root window.
+ Use XSetCloseDownMode to make the resource permanent.
5. Ungrab the server.
XSetRGBColormaps can generate ``BadAlloc'', ``BadAtom'', and ``BadWin-
dow'' 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 RGBCOLORMAP, 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. Other-
wise, 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 RGBDEFAULTMAP 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 func-
tion. The redmax, greenmax, and bluemax 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 redmax = 7, greenmax = 7, and bluemax = 3.
An alternate allocation that uses only 216 colors is redmax = 5,
greenmax = 5, and bluemax = 5.
The redmult, greenmult, and bluemult members give the scale factors
used to compose a full pixel value. (See the discussion of the
basepixel members for further information.) For a 3/3/2 allocation,
redmult might be 32, greenmult might be 4, and bluemult might be 1.
For a 6-colors-each allocation, redmult might be 36, greenmult might be
6, and bluemult might be 1.
The basepixel member gives the base pixel value used to compose a full
pixel value. Usually, the basepixel is obtained from a call to the XAl-
locColorPlanes 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, redmax, redmult, and
basepixel members are defined. The other members are ignored. To com-
pute 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 indi-
cates 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
RGBCOLORMAP.
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 Win-
dow.
See also
XAllocColor(XS), XCreateColormap(XS), XFree(XS), XSetCloseDownMode(XS)
Xlib - C Language X Interface