GetBitmap

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, Tk_GetBitmapFromData - maintain
       database of single-plane pixmaps

SYNOPSIS
       #include <tk.h>

       Pixmap                                                                  │
       Tk_GetBitmapFromObj(interp, tkwin, objPtr)                              │

       Pixmap                                                                  │
       Tk_GetBitmap(interp, tkwin, info)                                       │

       Pixmap                                                                  │
       Tk_GetBitmapFromObj(tkwin, objPtr)                                      │

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

       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 isn't        │
                                             cached.

       CONST char      *name       (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_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



Tk                                    8.1             Tk_AllocBitmapFromObj(3)