Tk_GetBitmap, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmap, Tk_GetBitmapFromData - maintain database of single-plane pixmaps
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)
- 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.
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.
75% gray: a checkerboard pattern where three out of four bits are on.
50% gray: a checkerboard pattern where every other bit is on.
25% gray: a checkerboard pattern where one out of every four bits 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.
In addition, the following pre-defined names are available only on the Macintosh platform:
A generic document.
The edition symbol.
Generic application icon.
A desk accessory.
Generic folder icon.
A locked folder.
A trash can.
A floppy disk.
A floppy disk with chip.
A cd disk icon.
A folder with prefs symbol.
A database document icon.
A stop sign.
A face with ballon words.
A triangle with an 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.