XGetRGBColormaps man page on BSDi

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XAllocStandardColormap(3X1XLIB FUNCTIXAllocStandardColormap(3X11)

NAME
       XAllocStandardColormap, XSetRGBColormaps, XGetRGBCol-
       ormaps, XStandardColormap - allocate, set, or read a stan-
       dard 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, XAlloc-
       StandardColormap 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

X Version 11		Release 6.4				1

XAllocStandardColormap(3X1XLIB FUNCTIXAllocStandardColormap(3X11)

       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 defini-
       tion.

       The XSetRGBColormaps function usually is only used by win-
       dow 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 XStan-
		 dardColormap structure.

	    o	Attach the property to the root window.

	    o	Use XSetCloseDownMode to make the resource per-
		 manent.

       5.   Ungrab the server.

       XSetRGBColormaps can generate BadAlloc, BadAtom, and Bad-
       Window 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

X Version 11		Release 6.4				2

XAllocStandardColormap(3X1XLIB FUNCTIXAllocStandardColormap(3X11)

       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 defini-
       tion.

       XGetRGBColormaps can generate BadAtom and BadWindow
       errors.

STRUCTURES
       The XStandardColormap structure contains:

       /* Hints */
       #define	ReleaseByFreeingCol-	( (XID)
		 ormap			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 XCre-
       ateColormap 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 col-
       ormap 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 alter-
       nate 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:

X Version 11		Release 6.4				3

XAllocStandardColormap(3X1XLIB FUNCTIXAllocStandardColormap(3X11)

       (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 effec-
       tively converts the resulting positive multiplier into a
       negative one.  The masking step will take place automati-
       cally 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 col-
       ormap 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 informa-
       tion 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

X Version 11		Release 6.4				4

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