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Tk_AllocBitmapFromObj, Tk_GetBitmap, Tk_GetBitmapFromObj, Tk_DefineBitmap, Tk_NameOfBitmap, Tk_SizeOfBitmap, Tk_FreeBitmapFromObj, Tk_FreeBitmap -
maintain database of single-plane pixmaps
#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)
| Type | Name | Mode |
|---|---|---|
| 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 void | *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. | ||
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:
In addition, the following pre-defined names are available only on the Macintosh platform:
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 interpreter interp's 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");
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.
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.