Tk_AllocBitmapFromObj(3) Tk Library Procedures Tk_AllocBitmapFromObj(3)______________________________________________________________________________NAME
Tk_AllocBitmapFromObj, Tk_GetBitmap, Tk_GetBitmapFromObj,
Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmapFro‐
mObj, Tk_FreeBitmap, Tk_GetBitmapFromData - maintain database of sin‐
gle-plane pixmaps
SYNOPSIS
#include <tk.h>
Pixmap │
Tk_GetBitmapFromObj(interp, tkwin, objPtr) │
Pixmap │
Tk_GetBitmap(interp, tkwin, info) │
Pixmap │
Tk_GetBitmapFromObj(tkwin, objPtr) │
int
Tk_DefineBitmap(interp, name, source, width, height)
char *
Tk_NameOfBitmap(display, bitmap)
Tk_SizeOfBitmap(display, bitmap, widthPtr, heightPtr)
Tk_FreeBitmapFromObj(tkwin, objPtr) │
Tk_FreeBitmap(display, bitmap)
ARGUMENTS
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 mod‐ │
ified to cache pointer to corre‐ │
sponding Pixmap. │
CONST char *info (in) │
Same as objPtr except description │
of bitmap is passed as a string │
and resulting Pixmap isn't │
cached.
CONST char *name (in) Name for new bitmap to be
defined.
char *source (in) Data for bitmap, in standard bit‐
map format. Must be stored in
static memory whose value will
never change.
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.
_________________________________________________________________DESCRIPTION
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 bit‐
maps to be named with character strings.
Tk_AllocBitmapFromObj returns a Pixmap identifier for a bitmap that │
matches the description in objPtr and is suitable for use in tkwin. It │
re-uses an existing bitmap, if possible, and creates a new one other‐ │
wise. ObjPtr's value must have one of the following forms:
@fileName FileName must be the name of a file containing a
bitmap description in the standard X11 or X10 for‐
mat.
name Name must be the name of a bitmap defined previ‐
ously with a call to Tk_DefineBitmap. The follow‐
ing names are pre-defined by Tk:
error The international "don't" symbol: a
circle with a diagonal 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 on.
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 it.
question A large question-mark.
warning A large exclamation point.
In addition, the following pre-defined names are
available only on the Macintosh platform:
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 ballon 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 │
isn't NULL. Tk_AllocBitmapFromObj caches information about the return │
value in objPtr, which speeds up future calls to procedures such as │
Tk_AllocBitmapFromObj and Tk_GetBitmapFromObj. │
Tk_GetBitmap is identical to Tk_AllocBitmapFromObj except that the │
description of the bitmap 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 │
doesn't 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_Get‐
Bitmap. 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 nor‐
mally 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 mes‐
sage is left in interp->result. Note: Tk_DefineBitmap expects the
memory pointed to by source to be static: Tk_DefineBitmap doesn't 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 pattern. The
following code uses Tk_DefineBitmap to define a new bitmap named foo: │
Pixmap bitmap; │
#include "stip.bitmap" │
Tk_DefineBitmap(interp, "foo", stip_bits, │
stip_width, stip_height); │
... │
bitmap = Tk_GetBitmap(interp, tkwin, "foo"); │
This code causes the bitmap file to be read at compile-time and incor‐
porates the bitmap information into the program's executable image.
The same bitmap file could be read at run-time using Tk_GetBitmap: │
Pixmap bitmap; │
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 creat‐
ing 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 modi‐
fied 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 bitmap 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 created 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.
BUGS
In determining whether an existing bitmap can be used to satisfy a new
request, Tk_AllocBitmapFromObj and Tk_GetBitmap consider only the imme‐
diate 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 cur‐
rent directory has changed, thereby causing the name to refer to a dif‐
ferent file.
KEYWORDS
bitmap, pixmap
Tk 8.1 Tk_AllocBitmapFromObj(3)
