'\" '\" Copyright (c) 1990, 1991 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" SCCS: @(#) GetColor.3 1.22 96/08/27 13:21:26 '\" .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