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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.

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'\" RCS: @(#) $Id: GetColor.3,v 1.1.1.1 2002-01-16 10:25:48 markom Exp $

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.so man.macros

.TH Tk_GetColor 3 4.0 Tk "Tk Library Procedures"

.BS

.SH NAME

Tk_GetColor, Tk_GetColorByValue, Tk_NameOfColor, Tk_FreeColor \- maintain database of colors

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

XColor *

\fBTk_GetColor\fR(\fIinterp, tkwin, nameId\fB)\fR

.sp

XColor *

\fBTk_GetColorByValue\fR(\fItkwin, prefPtr\fB)\fR

.sp

char *

\fBTk_NameOfColor(\fIcolorPtr\fB)\fR

.sp

GC

\fBTk_GCForColor\fR(\fIcolorPtr, drawable\fR)

.sp

\fBTk_FreeColor(\fIcolorPtr\fB)\fR

.SH ARGUMENTS

.AS "Tcl_Interp" *colorPtr

.AP Tcl_Interp *interp in

Interpreter to use for error reporting.

.AP Tk_Window tkwin in

Token for window in which color will be used.

.AP Tk_Uid nameId in

Textual description of desired color.

.AP XColor *prefPtr in

Indicates red, green, and blue intensities of desired

color.

.AP XColor *colorPtr in

Pointer to X color information.  Must have been allocated by previous

call to \fBTk_GetColor\fR or \fBTk_GetColorByValue\fR, except when passed

to \fBTk_NameOfColor\fR.

.AP 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.

.BE

.SH DESCRIPTION

.PP

The \fBTk_GetColor\fR and \fBTk_GetColorByValue\fR procedures

locate pixel values that may be used to render particular

colors in the window given by \fItkwin\fR.  In \fBTk_GetColor\fR

the desired color is specified with a Tk_Uid (\fInameId\fR), which

may have any of the following forms:

.TP 20

\fIcolorname\fR

Any of the valid textual names for a color defined in the

server's color database file, such as \fBred\fR or \fBPeachPuff\fR.

.TP 20

\fB#\fIRGB\fR

.TP 20

\fB#\fIRRGGBB\fR

.TP 20

\fB#\fIRRRGGGBBB\fR

.TP 20

\fB#\fIRRRRGGGGBBBB\fR

A numeric specification of the red, green, and blue intensities

to use to display the color.  Each \fIR\fR, \fIG\fR, or \fIB\fR

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.

.PP

In \fBTk_GetColorByValue\fR, the desired color is indicated with

the \fIred\fR, \fIgreen\fR, and \fIblue\fR fields of the structure

pointed to by \fIcolorPtr\fR.

.PP

If \fBTk_GetColor\fR or \fBTk_GetColorByValue\fR 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 limitations of the screen) and a pixel value

that may be used to draw in the color.

If the colormap for \fItkwin\fR is full, \fBTk_GetColor\fR

and \fBTk_GetColorByValue\fR will use the closest existing color

in the colormap.

If \fBTk_GetColor\fR encounters an error while allocating

the color (such as an unknown color name) then NULL is returned and

an error message is stored in \fIinterp->result\fR;

\fBTk_GetColorByValue\fR never returns an error.

.PP

\fBTk_GetColor\fR and \fBTk_GetColorByValue\fR maintain a database

of all the colors currently in use.

If the same \fInameId\fR is requested multiple times from

\fBTk_GetColor\fR (e.g. by different windows), or if the

same intensities are requested multiple times from

\fBTk_GetColorByValue\fR, then existing pixel values will

be re-used.  Re-using an existing pixel avoids any interaction

with the X server, which makes the allocation much more

efficient.  For this reason, you should generally use

\fBTk_GetColor\fR or \fBTk_GetColorByValue\fR

instead of Xlib procedures like \fBXAllocColor\fR,

\fBXAllocNamedColor\fR, or \fBXParseColor\fR.

.PP

Since different calls to \fBTk_GetColor\fR or \fBTk_GetColorByValue\fR

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

\fBXAllocColorCells\fR to allocate the pixel value for the color.

.PP

The procedure \fBTk_NameOfColor\fR is roughly the inverse of

\fBTk_GetColor\fR.  If its \fIcolorPtr\fR argument was created

by \fBTk_GetColor\fR, then the return value is the \fInameId\fR

string that was passed to \fBTk_GetColor\fR to create the

color.  If \fIcolorPtr\fR was created by a call to \fBTk_GetColorByValue\fR,

or by any other mechanism, then the return value is a string

that could be passed to \fBTk_GetColor\fR to return the same

color.  Note:  the string returned by \fBTk_NameOfColor\fR is

only guaranteed to persist until the next call to \fBTk_NameOfColor\fR.

.PP

\fBTk_GCForColor\fR returns a graphics context whose \fBForeground\fR

field is the pixel allocated for \fIcolorPtr\fR 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 \fIcolorPtr\fR exists;  it is freed when the last reference

to \fIcolorPtr\fR is freed by calling \fBTk_FreeColor\fR.

.PP

When a pixel value returned by \fBTk_GetColor\fR or

\fBTk_GetColorByValue\fR is no longer

needed, \fBTk_FreeColor\fR should be called to release the color.

There should be exactly one call to \fBTk_FreeColor\fR for

each call to \fBTk_GetColor\fR or \fBTk_GetColorByValue\fR.

When a pixel value is no longer in

use anywhere (i.e. it has been freed as many times as it has been gotten)

\fBTk_FreeColor\fR will release it to the X server and delete it from

the database.

.SH KEYWORDS

color, intensity, pixel value