Tk_AllocBitmapFromObj(3) Tk Library Procedures Tk_AllocBitmapFromObj(3)
Tk_AllocBitmapFromObj, Tk_GetBitmap, Tk_GetBitmapFromObj, Tk_DefineBitmap, Tk_NameOf-
Bitmap, Tk_SizeOfBitmap, Tk_FreeBitmapFromObj, Tk_FreeBitmap - maintain database of sin-
Tk_AllocBitmapFromObj(interp, tkwin, objPtr)
Tk_GetBitmap(interp, tkwin, info)
Tk_DefineBitmap(interp, name, source, width, height)
const char *
Tk_SizeOfBitmap(display, bitmap, widthPtr, heightPtr)
Tcl_Interp *interp (in) Interpreter to use for error reporting; if NULL then
no error message is left after errors.
Tk_Window tkwin (in) Token for window in which the bitmap will be used.
Tcl_Obj *objPtr (in/out) String value describes desired bitmap; internal rep
will be modified to cache pointer to corresponding
const char *info (in) Same as objPtr except description of bitmap is
passed as a string and resulting Pixmap is not
const char *name (in) Name for new bitmap to be defined.
const char *source (in) Data for bitmap, in standard bitmap format. Must be
stored in static memory whose value will never
int width (in) Width of bitmap.
int height (in) Height of bitmap.
int *widthPtr (out) Pointer to word to fill in with bitmap's width.
int *heightPtr (out) Pointer to word to fill in with bitmap's height.
Display *display (in) Display for which bitmap was allocated.
Pixmap bitmap (in) Identifier for a bitmap allocated by
Tk_AllocBitmapFromObj or Tk_GetBitmap.
These procedures manage a collection of bitmaps (one-plane pixmaps) being used by an
application. The procedures allow bitmaps to be re-used efficiently, thereby avoiding
server overhead, and also allow bitmaps to be named with character strings.
Tk_AllocBitmapFromObj returns a Pixmap identifier for a bitmap that matches the descrip-
tion in objPtr and is suitable for use in tkwin. It re-uses an existing bitmap, if possi-
ble, and creates a new one otherwise. ObjPtr's value must have one of the following
@fileName FileName must be the name of a file containing a bitmap description in
the standard X11 or X10 format.
name Name must be the name of a bitmap defined previously with a call to
Tk_DefineBitmap. The following names are pre-defined by Tk:
error The international "don't" symbol: a circle with a diago-
nal line across it.
gray75 75% gray: a checkerboard pattern where three out of four
bits are on.
gray50 50% gray: a checkerboard pattern where every other bit is
gray25 25% gray: a checkerboard pattern where one out of every
four bits is on.
gray12 12.5% gray: a pattern where one-eighth of the bits are on,
consisting of every fourth pixel in every other row.
hourglass An hourglass symbol.
info A large letter "i".
questhead The silhouette of a human head, with a question mark in
question A large question-mark.
warning A large exclamation point.
In addition, the following pre-defined names are available only on the
document A generic document.
stationery Document stationery.
edition The edition symbol.
application Generic application icon.
accessory A desk accessory.
folder Generic folder icon.
pfolder A locked folder.
trash A trash can.
floppy A floppy disk.
ramdisk A floppy disk with chip.
cdrom A cd disk icon.
preferences A folder with prefs symbol.
querydoc A database document icon.
stop A stop sign.
note A face with balloon words.
caution A triangle with an exclamation point.
Under normal conditions, Tk_AllocBitmapFromObj returns an identifier for the requested
bitmap. If an error occurs in creating the bitmap, such as when objPtr refers to a non-
existent file, then None is returned and an error message is left in interp's result if
interp is not NULL. Tk_AllocBitmapFromObj caches information about the return value in
objPtr, which speeds up future calls to procedures such as Tk_AllocBitmapFromObj and
Tk_GetBitmap is identical to Tk_AllocBitmapFromObj except that the description of the bit-
map is specified with a string instead of an object. This prevents Tk_GetBitmap from
caching the return value, so Tk_GetBitmap is less efficient than Tk_AllocBitmapFromObj.
Tk_GetBitmapFromObj returns the token for an existing bitmap, given the window and
description used to create the bitmap. Tk_GetBitmapFromObj does not actually create the
bitmap; the bitmap must already have been created with a previous call to
Tk_AllocBitmapFromObj or Tk_GetBitmap. The return value is cached in objPtr, which speeds
up future calls to Tk_GetBitmapFromObj with the same objPtr and tkwin.
Tk_DefineBitmap associates a name with in-memory bitmap data so that the name can be used
in later calls to Tk_AllocBitmapFromObj or Tk_GetBitmap. The nameId argument gives a name
for the bitmap; it must not previously have been used in a call to Tk_DefineBitmap. The
arguments source, width, and height describe the bitmap. Tk_DefineBitmap normally returns
TCL_OK; if an error occurs (e.g. a bitmap named nameId has already been defined) then
TCL_ERROR is returned and an error message is left in interp->result. Note:
Tk_DefineBitmap expects the memory pointed to by source to be static: Tk_DefineBitmap
does not make a private copy of this memory, but uses the bytes pointed to by source later
in calls to Tk_AllocBitmapFromObj or Tk_GetBitmap.
Typically Tk_DefineBitmap is used by #include-ing a bitmap file directly into a C program
and then referencing the variables defined by the file. For example, suppose there exists
a file stip.bitmap, which was created by the bitmap program and contains a stipple pat-
tern. The following code uses Tk_DefineBitmap to define a new bitmap named foo:
Tk_DefineBitmap(interp, "foo", stip_bits,
bitmap = Tk_GetBitmap(interp, tkwin, "foo");
This code causes the bitmap file to be read at compile-time and incorporates the bitmap
information into the program's executable image. The same bitmap file could be read at
run-time using Tk_GetBitmap:
bitmap = Tk_GetBitmap(interp, tkwin, "@stip.bitmap");
The second form is a bit more flexible (the file could be modified after the program has
been compiled, or a different string could be provided to read a different file), but it
is a little slower and requires the bitmap file to exist separately from the program.
Tk maintains a database of all the bitmaps that are currently in use. Whenever possible,
it will return an existing bitmap rather than creating a new one. When a bitmap is no
longer used, Tk will release it automatically. This approach can substantially reduce
server overhead, so Tk_AllocBitmapFromObj and Tk_GetBitmap should generally be used in
preference to Xlib procedures like XReadBitmapFile.
The bitmaps returned by Tk_AllocBitmapFromObj and Tk_GetBitmap are shared, so callers
should never modify them. If a bitmap must be modified dynamically, then it should be
created by calling Xlib procedures such as XReadBitmapFile or XCreatePixmap directly.
The procedure Tk_NameOfBitmap is roughly the inverse of Tk_GetBitmap. Given an X Pixmap
argument, it returns the textual description that was passed to Tk_GetBitmap when the bit-
map was created. Bitmap must have been the return value from a previous call to
Tk_AllocBitmapFromObj or Tk_GetBitmap.
Tk_SizeOfBitmap returns the dimensions of its bitmap argument in the words pointed to by
the widthPtr and heightPtr arguments. As with Tk_NameOfBitmap, bitmap must have been cre-
ated by Tk_AllocBitmapFromObj or Tk_GetBitmap.
When a bitmap is no longer needed, Tk_FreeBitmapFromObj or Tk_FreeBitmap should be called
to release it. For Tk_FreeBitmapFromObj the bitmap to release is specified with the same
information used to create it; for Tk_FreeBitmap the bitmap to release is specified with
its Pixmap token. There should be exactly one call to Tk_FreeBitmapFromObj or
Tk_FreeBitmap for each call to Tk_AllocBitmapFromObj or Tk_GetBitmap.
In determining whether an existing bitmap can be used to satisfy a new request,
Tk_AllocBitmapFromObj and Tk_GetBitmap consider only the immediate value of the string
description. For example, when a file name is passed to Tk_GetBitmap, Tk_GetBitmap will
assume it is safe to re-use an existing bitmap created from the same file name: it will
not check to see whether the file itself has changed, or whether the current directory has
changed, thereby causing the name to refer to a different file.
Tk 8.1 Tk_AllocBitmapFromObj(3)