archie/tk4.2/doc/GetBitmap.3

'\"
'\" Copyright (c) 1990 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" SCCS: @(#) GetBitmap.3 1.24 96/08/27 13:21:25
'\" 
.so man.macros
.TH Tk_GetBitmap 3 4.1 Tk "Tk Library Procedures"
.BS
.SH NAME
Tk_GetBitmap, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmap, Tk_GetBitmapFromData \- maintain database of single-plane pixmaps
.SH SYNOPSIS
.nf
\fB#include <tk.h>\fR
.sp
Pixmap
\fBTk_GetBitmap(\fIinterp, tkwin, id\fB)\fR
.sp
int
\fBTk_DefineBitmap(\fIinterp, nameId, source, width, height\fB)\fR
.sp
Tk_Uid
\fBTk_NameOfBitmap(\fIdisplay, bitmap\fB)\fR
.sp
\fBTk_SizeOfBitmap(\fIdisplay, bitmap, widthPtr, heightPtr\fB)\fR
.sp
\fBTk_FreeBitmap(\fIdisplay, bitmap\fB)\fR
.SH 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 \fIbitmap\fR's width.
.AP "int" *heightPtr out
Pointer to word to fill in with \fIbitmap\fR's height.
.AP Display *display in
Display for which \fIbitmap\fR was allocated.
.AP Pixmap bitmap in
Identifier for a bitmap allocated by \fBTk_GetBitmap\fR.
.BE

.SH DESCRIPTION
.PP
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.
.PP
\fBTk_GetBitmap\fR 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, \fIid\fR must have
one of the following forms:
.TP 20
\fB@\fIfileName\fR
\fIFileName\fR must be the name of a file containing a bitmap
description in the standard X11 or X10 format.
.TP 20
\fIname\fR
\fIName\fR must be the name of a bitmap defined previously with
a call to \fBTk_DefineBitmap\fR.  The following names are pre-defined
by Tk:
.RS
.TP 12
\fBerror\fR
The international "don't" symbol:  a circle with a diagonal line
across it.
.TP 12
\fBgray50\fR
50% gray: a checkerboard pattern where every other bit is on.
.TP 12
\fBgray12\fR
12.5% gray: a pattern where one-eighth of the bits are on, consisting of
every fourth pixel in every other row.
.TP 12
\fBhourglass\fR
An hourglass symbol.
.TP 12
\fBinfo\fR
A large letter ``i''.
.TP 12
\fBquesthead\fR
The silhouette of a human head, with a question mark in it.
.TP 12
\fBquestion\fR
A large question-mark.
.TP 12
\fBwarning\fR
A large exclamation point.
.RE
.LP
Under normal conditions, \fBTk_GetBitmap\fR
returns an identifier for the requested bitmap.  If an error
occurs in creating the bitmap, such as when \fIid\fR refers
to a non-existent file, then \fBNone\fR is returned and an error
message is left in \fIinterp->result\fR.
.PP
\fBTk_DefineBitmap\fR associates a name with
in-memory bitmap data so that the name can be used in later
calls to \fBTk_GetBitmap\fR.  The \fInameId\fR
argument gives a name for the bitmap;  it must not previously
have been used in a call to \fBTk_DefineBitmap\fR.
The arguments \fIsource\fR, \fIwidth\fR, and \fIheight\fR
describe the bitmap.
\fBTk_DefineBitmap\fR normally returns TCL_OK;  if an error occurs
(e.g. a bitmap named \fInameId\fR has already been defined) then
TCL_ERROR is returned and an error message is left in
\fIinterp->result\fR.
Note:  \fBTk_DefineBitmap\fR expects the memory pointed to by
\fIsource\fR to be static:  \fBTk_DefineBitmap\fR doesn't make
a private copy of this memory, but uses the bytes pointed to
by \fIsource\fR later in calls to \fBTk_GetBitmap\fR.
.PP
Typically \fBTk_DefineBitmap\fR is used by \fB#include\fR-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 \fBstip.bitmap\fR,
which was created by the \fBbitmap\fR program and contains
a stipple pattern.
The following code uses \fBTk_DefineBitmap\fR to define a
new bitmap named \fBfoo\fR:
.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 \fBTk_GetBitmap\fR:
.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.
.PP
\fBTk_GetBitmap\fR 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
\fBTk_GetBitmap\fR should generally be used in preference to Xlib
procedures like \fBXReadBitmapFile\fR.
.PP
The bitmaps returned by \fBTk_GetBitmap\fR
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 \fBXReadBitmapFile\fR
or \fBXCreatePixmap\fR directly.
.PP
The procedure \fBTk_NameOfBitmap\fR is roughly the inverse of
\fBTk_GetBitmap\fR.
Given an X Pixmap argument, it returns the \fIid\fR that was
passed to \fBTk_GetBitmap\fR when the bitmap was created.
\fIBitmap\fR must have been the return value from a previous
call to \fBTk_GetBitmap\fR.
.PP
\fBTk_SizeOfBitmap\fR returns the dimensions of its \fIbitmap\fR
argument in the words pointed to by the \fIwidthPtr\fR and
\fIheightPtr\fR arguments.  As with \fBTk_NameOfBitmap\fR,
\fIbitmap\fR must have been created by \fBTk_GetBitmap\fR.
.PP
When a bitmap returned by \fBTk_GetBitmap\fR
is no longer needed, \fBTk_FreeBitmap\fR should be called to release it.
There should be exactly one call to \fBTk_FreeBitmap\fR for
each call to \fBTk_GetBitmap\fR.
When a bitmap is no longer in use anywhere (i.e. it has been freed as
many times as it has been gotten) \fBTk_FreeBitmap\fR will release
it to the X server and delete it from the database.

.SH BUGS
In determining whether an existing bitmap can be used to satisfy
a new request, \fBTk_GetBitmap\fR
considers only the immediate value of its \fIid\fR argument.  For
example, when a file name is passed to \fBTk_GetBitmap\fR,
\fBTk_GetBitmap\fR 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.

.SH KEYWORDS
bitmap, pixmap