Tk_AllocBitmapFromObj(3)

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
Interpreter to use for error reporting; if NULL then no error message is left after errors. Token for window in which the bitmap will be used. String value describes desired bitmap; internal rep will be modified to cache pointer to corresponding Pixmap. Same as objPtr except description of bitmap is passed as a string and resulting Pixmap isn't cached. Name for new bitmap to be defined. Data for bitmap, in standard bitmap format. Must be stored in static memory whose value will never change. Width of bitmap. Height of bitmap. Pointer to word to fill in with bitmap's width. Pointer to word to fill in with bitmap's height. Display for which bitmap was allocated. Identifier for a bitmap allocated by Tk_AllocBitmapFromObj or 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_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 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.

    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 ballon 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 isn't 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 doesn't 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 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_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