Tk_AllocColorFromObj(3tk) Tk Library Procedures Tk_AllocColorFromObj(3tk)
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NAME
Tk_AllocColorFromObj, Tk_GetColor, Tk_GetColorFromObj, Tk_GetColorBy-
Value, Tk_NameOfColor, Tk_FreeColorFromObj, Tk_FreeColor - maintain
database of colors
SYNOPSIS
#include <tk.h>
XColor *
Tk_AllocColorFromObj(interp, tkwin, objPtr)
XColor *
Tk_GetColor(interp, tkwin, name)
XColor *
Tk_GetColorFromObj(tkwin, objPtr)
XColor *
Tk_GetColorByValue(tkwin, prefPtr)
const char *
Tk_NameOfColor(colorPtr)
GC
Tk_GCForColor(colorPtr, drawable)
Tk_FreeColorFromObj(tkwin, objPtr)
Tk_FreeColor(colorPtr)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for error report-
ing.
Tk_Window tkwin (in) Token for window in which color will
be used.
Tcl_Obj *objPtr (in/out) String value describes desired
color; internal rep will be modified
to cache pointer to corresponding
(XColor *).
char *name (in) Same as objPtr except description of
color is passed as a string and re-
sulting (XColor *) is not cached.
XColor *prefPtr (in) Indicates red, green, and blue in-
tensities of desired color.
XColor *colorPtr (in) Pointer to X color information.
Must have been allocated by previous
call to Tk_AllocColorFromObj,
Tk_GetColor or Tk_GetColorByValue,
except when passed to Tk_NameOf-
Color.
Drawable drawable (in) Drawable in which the result graph-
ics context will be used. Must have
same screen and depth as the window
for which the color was allocated.
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DESCRIPTION
These procedures manage the colors being used by a Tk application.
They allow colors to be shared whenever possible, so that colormap
space is preserved, and they pick closest available colors when col-
ormap space is exhausted.
Given a textual description of a color, Tk_AllocColorFromObj locates a
pixel value that may be used to render the color in a particular win-
dow. The desired color is specified with a value whose string value
must have one 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
PeachPuff.
#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 rep-
resent the most significant bits of the color,
while the lower unfilled bits will be repeatedly
replicated from the available higher bits. For ex-
ample, #3a7 is the same as #3333aaaa7777.
Tk_AllocColorFromObj 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 limitations
of the screen) and a pixel value that may be used to draw with the
color in tkwin. If an error occurs in Tk_AllocColorFromObj (such as an
unknown color name) then NULL is returned and an error message is
stored in interp's result if interp is not NULL. If the colormap for
tkwin is full, Tk_AllocColorFromObj will use the closest existing color
in the colormap. Tk_AllocColorFromObj caches information about the re-
turn value in objPtr, which speeds up future calls to procedures such
as Tk_AllocColorFromObj and Tk_GetColorFromObj.
Tk_GetColor is identical to Tk_AllocColorFromObj except that the de-
scription of the color is specified with a string instead of a value.
This prevents Tk_GetColor from caching the return value, so Tk_GetColor
is less efficient than Tk_AllocColorFromObj.
Tk_GetColorFromObj returns the token for an existing color, given the
window and description used to create the color. Tk_GetColorFromObj
does not actually create the color; the color must already have been
created with a previous call to Tk_AllocColorFromObj or Tk_GetColor.
The return value is cached in objPtr, which speeds up future calls to
Tk_GetColorFromObj with the same objPtr and tkwin.
Tk_GetColorByValue is similar to Tk_GetColor except that the desired
color is indicated with the red, green, and blue fields of the struc-
ture pointed to by colorPtr.
This package maintains a database of all the colors currently in use.
If the same color is requested multiple times from Tk_GetColor or
Tk_AllocColorFromObj (e.g. by different windows), or if the same inten-
sities are requested multiple times from Tk_GetColorByValue, then ex-
isting pixel values will be re-used. Re-using an existing pixel avoids
any interaction with the window server, which makes the allocation much
more efficient. These procedures also provide a portable interface
that works across all platforms. For this reason, you should generally
use Tk_AllocColorFromObj, Tk_GetColor, or Tk_GetColorByValue instead of
lower level procedures like XAllocColor.
Since different calls to this package may return the same shared pixel
value, callers should never change the color of a pixel returned by the
procedures. 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_AllocColorFromObj or Tk_Get-
Color then the return value is the string that was used 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 re-
turned by Tk_NameOfColor is only guaranteed to persist until the next
call to Tk_NameOfColor.
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 colorPtr exists; it is freed when the last reference to col-
orPtr is freed by calling Tk_FreeColor.
When a color is no longer needed Tk_FreeColorFromObj or Tk_FreeColor
should be called to release it. For Tk_FreeColorFromObj the color to
release is specified with the same information used to create it; for
Tk_FreeColor the color to release is specified with a pointer to its
XColor structure. There should be exactly one call to Tk_FreeColorFro-
mObj or Tk_FreeColor for each call to Tk_AllocColorFromObj, Tk_Get-
Color, or Tk_GetColorByValue.
KEYWORDS
color, intensity, value, pixel value
Tk 8.1 Tk_AllocColorFromObj(3tk)
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