Tk_GetColor
Tk_AllocColorFromObj(3) Tk Library Procedures Tk_AllocColorFromObj(3)
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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)
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 |
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 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 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
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. For
example, #3a7 is the same as #3000a0007000.
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 isn't 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 |
return 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 |
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 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
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 window server, which makes the alloca-
tion 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
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 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, object, pixel value
Tk 8.1 Tk_AllocColorFromObj(3)
