Tk_AllocFontFromObj - Man Page

maintain database of fonts


#include <tk.h>

Tk_AllocFontFromObj(interp, tkwin, objPtr)

Tk_GetFont(interp, tkwin, string)

Tk_GetFontFromObj(tkwin, objPtr)

const char *

Tk_FreeFontFromObj(tkwin, objPtr)



Tcl_Interp *interp (in)

Interpreter to use for error reporting.  If NULL, then no error messages are left after errors.

Tk_Window tkwin (in)

Token for window in which font will be used.

Tcl_Obj *objPtr (in/out)

Gives name or description of font.  See documentation for the font command for details on acceptable formats. Internal rep will be modified to cache corresponding Tk_Font.

const char *string (in)

Same as objPtr except description of font is passed as a string and resulting Tk_Font is not cached.

Tk_Font tkfont (in)

Opaque font token.


Tk_AllocFontFromObj finds the font indicated by objPtr and returns a token that represents the font.  The return value can be used in subsequent calls to procedures such as Tk_GetFontMetrics, Tk_MeasureChars, and Tk_FreeFont.  The Tk_Font token will remain valid until Tk_FreeFontFromObj or Tk_FreeFont is called to release it. ObjPtr can contain either a symbolic name or a font description; see the documentation for the font command for a description of the valid formats.  If Tk_AllocFontFromObj is unsuccessful (because, for example, objPtr did not contain a valid font specification) then it returns NULL and leaves an error message in interp's result if interp is not NULL.  Tk_AllocFontFromObj caches information about the return value in objPtr, which speeds up future calls to procedures such as Tk_AllocFontFromObj and Tk_GetFontFromObj.

Tk_GetFont is identical to Tk_AllocFontFromObj except that the description of the font is specified with a string instead of an object.  This prevents Tk_GetFont from caching the matching Tk_Font, so Tk_GetFont is less efficient than Tk_AllocFontFromObj.

Tk_GetFontFromObj returns the token for an existing font, given the window and description used to create the font. Tk_GetFontFromObj does not actually create the font; the font must already have been created with a previous call to Tk_AllocFontFromObj or Tk_GetFont.  The return value is cached in objPtr, which speeds up future calls to Tk_GetFontFromObj with the same objPtr and tkwin.

Tk_AllocFontFromObj and Tk_GetFont maintain a database of all fonts they have allocated.  If the same font is requested multiple times (e.g. by different windows or for different purposes), then a single Tk_Font will be shared for all uses.  The underlying resources will be freed automatically when no-one is using the font anymore.

The procedure Tk_NameOfFont is roughly the inverse of Tk_GetFont.  Given a tkfont that was created by Tk_GetFont (or Tk_AllocFontFromObj), the return value is the string argument that was passed to Tk_GetFont to create the font.  The string returned by Tk_NameOfFont is only guaranteed to persist until the tkfont is deleted.  The caller must not modify this string.

When a font is no longer needed, Tk_FreeFontFromObj or Tk_FreeFont should be called to release it.  For Tk_FreeFontFromObj the font to release is specified with the same information used to create it; for Tk_FreeFont the font to release is specified with its Tk_Font token.  There should be exactly one call to Tk_FreeFontFromObj or Tk_FreeFont for each call to Tk_AllocFontFromObj or Tk_GetFont.

See Also




Referenced By

The man pages Tk_FreeFont(3), Tk_FreeFontFromObj(3), Tk_GetFont(3), Tk_GetFontFromObj(3) and Tk_NameOfFont(3) are aliases of Tk_AllocFontFromObj(3).

8.1 Tk Library Procedures