Tk_GetColor (3)
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" *colorPtr
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 previous
call to Tk_GetColor or Tk_GetColorByValue, except when passed
to Tk_NameOfColor.
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.
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 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 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 limitations 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 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 existing pixel avoids any interaction
with the X server, which makes the allocation much more
efficient. For this reason, you should generally use
Tk_GetColor or Tk_GetColorByValue
instead of Xlib procedures like XAllocColor,
XAllocNamedColor, 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 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_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_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 colorPtr is freed by calling Tk_FreeColor.
When a pixel value returned by Tk_GetColor or
Tk_GetColorByValue 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_GetColorByValue.
When a pixel value is no longer in
use anywhere (i.e. it has been freed as many times as it has been gotten)
Tk_FreeColor will release it to the X server and delete it from
the database.
KEYWORDS
color, intensity, pixel value
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