Tribblix: manual page: Tk_GetBitmapFromObj.3

Tk_AllocBitmapFromObj(3) Tk Library Procedures Tk_AllocBitmapFromObj(3)

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NAME

Tk_AllocBitmapFromObj, Tk_GetBitmap, Tk_GetBitmapFromObj,
Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap,
Tk_FreeBitmapFromObj, Tk_FreeBitmap - maintain database of single-
plane pixmaps

SYNOPSIS

#include <tk.h>

Pixmap
Tk_AllocBitmapFromObj(interp, tkwin, objPtr)

Pixmap
Tk_GetBitmap(interp, tkwin, info)

Pixmap
Tk_GetBitmapFromObj(tkwin, objPtr)

int
Tk_DefineBitmap(interp, name, source, width, height)

const 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
modified to cache pointer to
corresponding Pixmap.

const char *info (in) Same as objPtr except
description of bitmap is passed
as a string and resulting
Pixmap is not cached.

const char *name (in) Name for new bitmap to be
defined.

const void *source (in) Data for bitmap, in standard
bitmap 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.
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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_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
otherwise. 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 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 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 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_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 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 interpreter interp's 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
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
incorporates 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
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 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
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.

KEYWORDS

bitmap, pixmap

Tk 8.1 Tk_AllocBitmapFromObj(3)