Tk4.2 C API Man Page -- GetBitmap (n)
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Tk_GetBitmap, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmap, Tk_GetBitmapFromData - maintain database of single-plane pixmaps


#include <tk.h>

Tk_GetBitmap(interp, tkwin, id)

Tk_DefineBitmap(interp, nameId, source, width, height)

Tk_NameOfBitmap(display, bitmap)

Tk_SizeOfBitmap(display, bitmap, widthPtr, heightPtr)

Tk_FreeBitmap(display, bitmap)


*interp (in) Interpreter to use for error reporting.

tkwin (in) Token for window in which the bitmap will be used.

id (in) Description of bitmap; see below for possible values.

nameId (in) Name for new bitmap to be defined.

*source (in) Data for bitmap, in standard bitmap format. Must be stored in static memory whose value will never change.

width (in) Width of bitmap.

height (in) Height of bitmap.

*widthPtr (out) Pointer to word to fill in with bitmap's width.

*heightPtr (out) Pointer to word to


*display (in) Display for which bit_map was allocated.

bitmap (in) Identifier for a bitmap allocated by 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_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:

FileName must be the name of a file containing a bitmap description in the standard X11 or X10 format.

Name must be the name of a bitmap defined previously with a call to Tk_DefineBitmap. The following names are pre-defined by Tk:

The international "don't" symbol: a circle with a diagonal line across it.

50% gray: a checkerboard pattern where every other bit is on.

12.5% gray: a pattern where one-eighth of the bits are on, consisting of every fourth pixel in every other row.

An hourglass symbol.

A large letter ``i''.

The silhouette of a human head, with a question mark in it.

A large question-mark.

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: 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")); 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, Tk_GetUid("@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_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.


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.


bitmap, pixmap

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