Tk_AllocFontFromObj(3) Tk Library Procedures Tk_AllocFontFromObj(3)
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NAME
Tk_AllocFontFromObj, Tk_GetFont, Tk_GetFontFromObj, Tk_NameOfFont, Tk_FreeFontFromObj, Tk_FreeFont - maintain database of fonts
SYNOPSIS
#include <tk.h>
Tk_Font
Tk_AllocFontFromObj(interp, tkwin, objPtr)
Tk_Font
Tk_GetFont(interp, tkwin, string)
Tk_Font
Tk_GetFontFromObj(tkwin, objPtr)
const char *
Tk_NameOfFont(tkfont)
Tk_Font
Tk_FreeFontFromObj(tkwin, objPtr)
void
Tk_FreeFont(tkfont)
ARGUMENTS
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 for-
mats. 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.
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DESCRIPTION
Tk_AllocFontFromObj finds the font indicated by objPtr and returns a token that represents the font. The return value can be used in sub-
sequent 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 docu-
mentation 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
Tk_FontId(3)
KEYWORDS
font
Tk 8.1 Tk_AllocFontFromObj(3)