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 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:

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 interp->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");

Pixmap bitmap;
bitmap = Tk_GetBitmap(interp, tkwin, "@stip.bitmap");

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