libtk/doc/GetBitmap.3

#include <tk.h>
Pixmap
Tk_GetBitmap(interp, tkwin, id)
int
Tk_DefineBitmap(interp, nameId, source, width, height)
Tk_Uid
Tk_NameOfBitmap(display, bitmap)
Tk_SizeOfBitmap(display, bitmap, widthPtr, heightPtr)
Tk_FreeBitmap(display, bitmap)
 ARGUMENTS
.AS "unsigned long" *pixelPtr
.AP Tcl_Interp *interp in
Interpreter to use for error reporting.
.AP Tk_Window tkwin in
Token for window in which the bitmap will be used.
.AP Tk_Uid id in
Description of bitmap; see below for possible values.
.AP Tk_Uid nameId in
Name for new bitmap to be defined.
.AP char *source in
Data for bitmap, in standard bitmap format.
Must be stored in static memory whose value will never change.
.AP "int" width in
Width of bitmap.
.AP "int" height in
Height of bitmap.
.AP "int" *widthPtr out
Pointer to word to fill in with bitmap's width.
.AP "int" *heightPtr out
Pointer to word to fill in with bitmap's height.
.AP Display *display in
Display for which bitmap was allocated.
.AP Pixmap bitmap in
Identifier for a bitmap allocated by Tk_GetBitmap.
E
 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 bitmaps to be named with character strings.

Tk_GetBitmap takes as argument a Tk_Uid describing a bitmap.
It returns a Pixmap identifier for a bitmap corresponding to the
description. It re-uses an existing bitmap, if possible, and
creates a new one otherwise. At present, id must have
one of the following forms:
 20
@fileName
FileName must be the name of a file containing a bitmap
description in the standard X11 or X10 format.
 20
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:

 12
error
The international "don't" symbol: a circle with a diagonal line
across it.
 12
gray50
50% gray: a checkerboard pattern where every other bit is on.
 12
gray12
12.5% gray: a pattern where one-eighth of the bits are on, consisting of
every fourth pixel in every other row.
 12
hourglass
An hourglass symbol.
 12
info
A large letter ``i''.
 12
questhead
The silhouette of a human head, with a question mark in it.
 12
question
A large question-mark.
 12
warning
A large exclamation point.


Under normal conditions, Tk_GetBitmap
returns an identifier for the requested bitmap. If an error
occurs in creating the bitmap, such as when id refers
to a non-existent file, then None is returned and an error
message is left in interp->result.

Tk_DefineBitmap associates a name with
in-memory bitmap data so that the name can be used in later
calls to 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 doesn't make
a private copy of this memory, but uses the bytes pointed to
by source later in calls to 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:
.CS
Pixmap bitmap;
#include "stip.bitmap"
Tk_DefineBitmap(interp, Tk_GetUid("foo"), stip_bits,
 stip_width, stip_height);
...
bitmap = Tk_GetBitmap(interp, tkwin, Tk_GetUid("foo"));
.CE
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:
.CS
Pixmap bitmap;
bitmap = Tk_GetBitmap(interp, tkwin, Tk_GetUid("@stip.bitmap"));
.CE
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_GetBitmap 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.
This approach can substantially reduce server overhead, so
Tk_GetBitmap should generally be used in preference to Xlib
procedures like XReadBitmapFile.

The bitmaps returned by 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 id that was
passed to Tk_GetBitmap when the bitmap was created.
Bitmap must have been the return value from a previous
call to 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_GetBitmap.

When a bitmap returned by Tk_GetBitmap
is no longer needed, Tk_FreeBitmap should be called to release it.
There should be exactly one call to Tk_FreeBitmap for
each call to Tk_GetBitmap.
When a bitmap is no longer in use anywhere (i.e. it has been freed as
many times as it has been gotten) Tk_FreeBitmap will release
it to the X server and delete it from the database.

 BUGS
In determining whether an existing bitmap can be used to satisfy
a new request, Tk_GetBitmap
considers only the immediate value of its id argument. 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.

 KEYWORDS
bitmap, pixmap