Tk_AllocFontFromObj(3) Tk Library Procedures Tk_AllocFontFromObj(3)
Tk_AllocFontFromObj, Tk_GetFont, Tk_GetFontFromObj, Tk_NameOfFont, Tk_FreeFontFromObj,
Tk_FreeFont - maintain database of fonts
Tk_AllocFontFromObj(interp, tkwin, objPtr)
Tk_GetFont(interp, tkwin, string)
const char *
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
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_Get-
FontMetrics, 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 pro-
cedures 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
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 infor-
mation 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.
Tk 8.1 Tk_AllocFontFromObj(3)