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Tk_GetColor(3)	      Tk Library Procedures	   Tk_GetColor(3)

_________________________________________________________________

NAME
       Tk_GetColor,  Tk_GetColorByValue, Tk_NameOfColor, Tk_Free-
       Color - maintain database of colors

SYNOPSIS
       #include <tk.h>

       XColor *
       Tk_GetColor(interp, tkwin, nameId)

       XColor *
       Tk_GetColorByValue(tkwin, prefPtr)

       char *
       Tk_NameOfColor(colorPtr)

       GC
       Tk_GCForColor(colorPtr, drawable)

       Tk_FreeColor(colorPtr)

ARGUMENTS
       Tcl_Interp   *interp	(in)	  Interpreter to use  for
					  error reporting.

       Tk_Window    tkwin	(in)	  Token	  for  window  in
					  which	 color	will   be
					  used.

       Tk_Uid	    nameId	(in)	  Textual  description of
					  desired color.

       XColor	    *prefPtr	(in)	  Indicates  red,  green,
					  and blue intensities of
					  desired color.

       XColor	    *colorPtr	(in)	  Pointer  to	X   color
					  information.	Must have
					  been allocated by  pre-
					  vious	 call  to Tk_Get-
					  Color or Tk_GetColorBy-
					  Value,    except   when
					  passed  to   Tk_NameOf-
					  Color.

       Drawable	    drawable	(in)	  Drawable  in	which the
					  result graphics context
					  will	 be  used.   Must
					  have	same  screen  and
					  depth as the window for
					  which	 the  color   was
					  allocated.

Tk			       4.0				1

Tk_GetColor(3)	      Tk Library Procedures	   Tk_GetColor(3)

_________________________________________________________________

DESCRIPTION
       The  Tk_GetColor	 and Tk_GetColorByValue procedures locate
       pixel values that may be used to render particular  colors
       in  the window given by tkwin.  In Tk_GetColor the desired
       color is specified with a Tk_Uid (nameId), which may  have
       any of the following forms:

       colorname	   Any	of  the valid textual names for a
			   color defined in  the  server's  color
			   database  file,  such as red or Peach-
			   Puff.

       #RGB

       #RRGGBB

       #RRRGGGBBB

       #RRRRGGGGBBBB	   A numeric specification  of	the  red,
			   green,  and blue intensities to use to
			   display the color.  Each R,	G,  or	B
			   represents a single hexadecimal digit.
			   The four forms  permit  colors  to  be
			   specified with 4-bit, 8-bit, 12-bit or
			   16-bit values.   When  fewer	 than  16
			   bits are provided for each color, they
			   represent the most significant bits of
			   the	color.	 For example, #3a7 is the
			   same as #3000a0007000.

       In Tk_GetColorByValue, the desired color is indicated with
       the  red,  green, and blue fields of the structure pointed
       to by colorPtr.

       If Tk_GetColor  or  Tk_GetColorByValue  is  successful  in
       allocating the desired color, then it returns a pointer to
       an XColor structure;  the structure  indicates  the  exact
       intensities  of	the  allocated	color  (which  may differ
       slightly from those requested, depending	 on  the  limita-
       tions of the screen) and a pixel value that may be used to
       draw in the color.  If the colormap  for	 tkwin	is  full,
       Tk_GetColor  and	 Tk_GetColorByValue  will use the closest
       existing color in the colormap.	If Tk_GetColor encounters
       an  error  while	 allocating the color (such as an unknown
       color name) then NULL is returned and an error message  is
       stored in interp->result; Tk_GetColorByValue never returns
       an error.

       Tk_GetColor and Tk_GetColorByValue maintain a database  of
       all  the	 colors	 currently in use.  If the same nameId is
       requested  multiple  times  from	 Tk_GetColor   (e.g.   by

Tk			       4.0				2

Tk_GetColor(3)	      Tk Library Procedures	   Tk_GetColor(3)

       different   windows),  or  if  the  same	 intensities  are
       requested multiple  times  from	Tk_GetColorByValue,  then
       existing pixel values will be re-used.  Re-using an exist-
       ing pixel avoids any interaction with the X server,  which
       makes  the  allocation much more efficient.  For this rea-
       son, you should generally use Tk_GetColor or  Tk_GetColor-
       ByValue	instead of Xlib procedures like XAllocColor, XAl-
       locNamedColor, or XParseColor.

       Since different calls to Tk_GetColor or Tk_GetColorByValue
       may  return  the	 same  shared pixel value, callers should
       never change the color of a pixel returned by  the  proce-
       dures.	If  you need to change a color value dynamically,
       you should use  XAllocColorCells	 to  allocate  the  pixel
       value for the color.

       The  procedure  Tk_NameOfColor  is  roughly the inverse of
       Tk_GetColor.  If its  colorPtr  argument	 was  created  by
       Tk_GetColor,  then  the	return value is the nameId string
       that was passed to Tk_GetColor to create	 the  color.   If
       colorPtr	 was  created by a call to Tk_GetColorByValue, or
       by any other mechanism, then the return value is a  string
       that  could  be	passed	to Tk_GetColor to return the same
       color.  Note:  the string returned  by  Tk_NameOfColor  is
       only guaranteed to persist until the next call to Tk_Name-
       OfColor.

       Tk_GCForColor returns a graphics context whose  Foreground
       field  is the pixel allocated for colorPtr and whose other
       fields all have default values.	This provides an easy way
       to do basic drawing with a color.  The graphics context is
       cached with the color and will exist only as long as  col-
       orPtr exists;  it is freed when the last reference to col-
       orPtr is freed by calling Tk_FreeColor.

       When a pixel value returned by Tk_GetColor or Tk_GetColor-
       ByValue is no longer needed, Tk_FreeColor should be called
       to release the color.  There should be exactly one call to
       Tk_FreeColor  for each call to Tk_GetColor or Tk_GetColor-
       ByValue.	 When a pixel value is no longer in use	 anywhere
       (i.e.  it has been freed as many times as it has been got-
       ten) Tk_FreeColor will release it  to  the  X  server  and
       delete it from the database.

KEYWORDS
       color, intensity, pixel value

Tk			       4.0				3

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