Tk_GetColor, Tk_GetColorByValue, Tk_NameOfColor Tk_FreeColor - maintain database of colors

SYNOPSIS

#include <tk.h>


XColor *
Tk_GetColor(interp, tkwin, colorMap, nameId)


XColor *
Tk_GetColorByValue(interp, tkwin, colorMap, prefPtr)


char *
Tk_NameOfColor(colorPtr)


Tk_FreeColor(colorPtr)

ARGUMENTS

Tk_Window tkwin (in)

Token for window in which color will be used.

Colormap colormap (in)

Colormap from which to allocate color. If None, then the default colormap for tkwin's screen is 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.

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 using the colormap given by colormap. 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 from colormap that may be used to draw in the color. If an error occurs in allocating a color then NULL is returned and an error message will be stored in interp->result.

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.

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