tk_alloccolorfromobj(3)

NAME

Tk_AllocColorFromObj, Tk_GetColor, Tk_GetColorFromObj,
Tk_GetColorByValue, 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 reporting.

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 corre
sponding (XColor *).

char *name (in)

Same as objPtr except description of color is
passed as a string and
resulting (XColor *)
isn't cached.

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_AllocColorFromObj, Tk_GetColor or Tk_Get ColorByValue, except when passed to Tk_Name OfColor.

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

These procedures manage the colors being used by a Tk
application. They allow colors to be shared whenever pos
sible, so that colormap space is preserved, and they pick
closest available colors when colormap space is exhausted.

Given a textual description of a color, Tk_AllocColorFro mObj locates a pixel value that may be used to render the
color in a particular window. The desired color is speci
fied with an object 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 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.

Tk_AllocColorFromObj returns a pointer to an XColor struc ture; 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 isn't NULL. If the colormap for tkwin is full, Tk_AllocColor FromObj will use the closest existing color in the col ormap. Tk_AllocColorFromObj caches information about the return value in objPtr, which speeds up future calls to procedures such as Tk_AllocColorFromObj and Tk_GetColor FromObj.

Tk_GetColor is identical to Tk_AllocColorFromObj except that the description of the color is specified with a
string instead of an object. 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 doesn't 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 structure pointed to by colorPtr.

This package maintains a database of all the colors cur
rently 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 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 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 gener
ally use Tk_AllocColorFromObj, Tk_GetColor, or Tk_GetCol orByValue instead of lower level procedures like XAlloc Color.

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 XAlloc
ColorCells 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_GetColor then the return value is the string that was used to create the color. If col_
orPtr 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 color is no longer needed Tk_FreeColorFromObj or Tk_FreeColor should be called to release it. For Tk_Free ColorFromObj 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_Free ColorFromObj or Tk_FreeColor for each call to Tk_AllocCol orFromObj, Tk_GetColor, or Tk_GetColorByValue.

KEYWORDS

color, intensity, object, pixel value

Tk 8.1 Tk_AllocColorFromObj(3)