Tribblix: manual page: XAllocStandardColormap.3

XAllocStandardColormap(3) XLIB FUNCTIONS XAllocStandardColormap(3)

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:

+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, 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