maintain database of single-plane pixmaps

## NAME

Tk_GetBitmap, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmap, Tk_GetBitmapFromData - maintain database of single-plane pixmaps

## SYNOPSIS

#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

`Tcl_Interp *interp` (in)
  Interpreter to use for error reporting.
`Tk_Window tkwin` (in)
  Token for window in which the bitmap will be used.
`Tk_Uid id` (in)
  Description of bitmap; see below for possible values.
`Tk_Uid *nameId` (in)
  Name for new bitmap to be defined.
`char *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_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 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
  FileName must be the name of a file containing a bitmap description in the standard X11 or X10 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.
gray50
  50% gray: a checkerboard pattern where every other bit is on.
gray25
  25% gray: a pattern where 25% of the bits are on, consisting of all the bit positions that can be reached by a chess knight starting at (0,0).
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.

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.

## 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