XAllocStandardColormap(3X11)X Version 11(Release 5)XAllocStandardColormap(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 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.
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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
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:
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/* 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
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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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