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
- 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(3), XCreateColormap(3), XFree(3), XSetCloseDownMode(3)
Xlib - C Language X Interface