Provided by: tk8.6-doc_8.6.14-1build1_all 
NAME
Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj, Tk_GetCursorFromData, Tk_NameOfCursor,
Tk_FreeCursorFromObj, Tk_FreeCursor - maintain database of cursors
SYNOPSIS
#include <tk.h>
Tk_Cursor
Tk_AllocCursorFromObj(interp, tkwin, objPtr)
Tk_Cursor
Tk_GetCursor(interp, tkwin, name)
Tk_Cursor
Tk_GetCursorFromObj(tkwin, objPtr)
Tk_Cursor
Tk_GetCursorFromData(interp, tkwin, source, mask, width, height, xHot, yHot, fg, bg)
const char *
Tk_NameOfCursor(display, cursor)
Tk_FreeCursorFromObj(tkwin, objPtr)
Tk_FreeCursor(display, cursor)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for error reporting.
Tk_Window tkwin (in) Token for window in which the cursor will be used.
Tcl_Obj *objPtr (in/out) Description of cursor; see below for possible values. Internal
rep will be modified to cache pointer to corresponding Tk_Cursor.
char *name (in) Same as objPtr except description of cursor is passed as a string
and resulting Tk_Cursor is not cached.
const char *source (in) Data for cursor cursor, in standard cursor format.
const char *mask (in) Data for mask cursor, in standard cursor format.
int width (in) Width of source and mask.
int height (in) Height of source and mask.
int xHot (in) X-location of cursor hot-spot.
int yHot (in) Y-location of cursor hot-spot.
Tk_Uid fg (in) Textual description of foreground color for cursor.
Tk_Uid bg (in) Textual description of background color for cursor.
Display *display (in) Display for which cursor was allocated.
Tk_Cursor cursor (in) Opaque Tk identifier for cursor. If passed to Tk_FreeCursor, must
have been returned by some previous call to Tk_GetCursor or
Tk_GetCursorFromData.
________________________________________________________________________________________________________________
DESCRIPTION
These procedures manage a collection of cursors being used by an application. The procedures allow
cursors to be re-used efficiently, thereby avoiding server overhead, and also allow cursors to be named
with character strings.
Tk_AllocCursorFromObj takes as argument an object describing a cursor, and returns an opaque Tk
identifier for a cursor corresponding to the description. It re-uses an existing cursor if possible and
creates a new one otherwise. Tk_AllocCursorFromObj caches information about the return value in objPtr,
which speeds up future calls to procedures such as Tk_AllocCursorFromObj and Tk_GetCursorFromObj. If an
error occurs in creating the cursor, such as when objPtr refers to a non-existent file, then None is
returned and an error message will be stored in interp's result if interp is not NULL. ObjPtr must
contain a standard Tcl list with one of the following forms:
name [fgColor [bgColor]]
Name is the name of a cursor in the standard X cursor cursor, i.e., any of the names defined in
cursorcursor.h, without the XC_. Some example values are X_cursor, hand2, or left_ptr. Appendix
B of “The X Window System” by Scheifler & Gettys has illustrations showing what each of these
cursors looks like. If fgColor and bgColor are both specified, they give the foreground and
background colors to use for the cursor (any of the forms acceptable to Tk_GetColor may be used).
If only fgColor is specified, then there will be no background color: the background will be
transparent. If no colors are specified, then the cursor will use black for its foreground color
and white for its background color.
The Macintosh version of Tk supports all of the X cursors and will also accept any of the standard
Mac cursors including ibeam, crosshair, watch, plus, and arrow. In addition, Tk will load
Macintosh cursor resources of the types crsr (color) and CURS (black and white) by the name of the
resource. The application and all its open dynamic library's resource files will be searched for
the named cursor. If there are conflicts color cursors will always be loaded in preference to
black and white cursors.
@sourceName maskName fgColor bgColor
In this form, sourceName and maskName are the names of files describing cursors for the cursor's
source bits and mask. Each file must be in standard X11 cursor format. FgColor and bgColor
indicate the colors to use for the cursor, in any of the forms acceptable to Tk_GetColor. This
form of the command will not work on Macintosh or Windows computers.
@sourceName fgColor
This form is similar to the one above, except that the source is used as mask also. This means
that the cursor's background is transparent. This form of the command will not work on Macintosh
or Windows computers.
@sourceName
This form only works on Windows, and will load a Windows system cursor (.ani or .cur) from the
file specified in sourceName.
Tk_GetCursor is identical to Tk_AllocCursorFromObj except that the description of the cursor is specified
with a string instead of an object. This prevents Tk_GetCursor from caching the return value, so
Tk_GetCursor is less efficient than Tk_AllocCursorFromObj.
Tk_GetCursorFromObj returns the token for an existing cursor, given the window and description used to
create the cursor. Tk_GetCursorFromObj does not actually create the cursor; the cursor must already have
been created with a previous call to Tk_AllocCursorFromObj or Tk_GetCursor. The return value is cached
in objPtr, which speeds up future calls to Tk_GetCursorFromObj with the same objPtr and tkwin.
Tk_GetCursorFromData allows cursors to be created from in-memory descriptions of their source and mask
cursors. Source points to standard cursor data for the cursor's source bits, and mask points to standard
cursor data describing which pixels of source are to be drawn and which are to be considered transparent.
Width and height give the dimensions of the cursor, xHot and yHot indicate the location of the cursor's
hot-spot (the point that is reported when an event occurs), and fg and bg describe the cursor's
foreground and background colors textually (any of the forms suitable for Tk_GetColor may be used).
Typically, the arguments to Tk_GetCursorFromData are created by including a cursor file directly into the
source code for a program, as in the following example:
Tk_Cursor cursor;
#include "source.cursor"
#include "mask.cursor"
cursor = Tk_GetCursorFromData(interp, tkwin, source_bits,
mask_bits, source_width, source_height, source_x_hot,
source_y_hot, Tk_GetUid("red"), Tk_GetUid("blue"));
Under normal conditions Tk_GetCursorFromData will return an identifier for the requested cursor. If an
error occurs in creating the cursor then None is returned and an error message will be stored in interp's
result.
Tk_AllocCursorFromObj, Tk_GetCursor, and Tk_GetCursorFromData maintain a database of all the cursors they
have created. Whenever possible, a call to Tk_AllocCursorFromObj, Tk_GetCursor, or Tk_GetCursorFromData
will return an existing cursor rather than creating a new one. This approach can substantially reduce
server overhead, so the Tk procedures should generally be used in preference to Xlib procedures like
XCreateFontCursor or XCreatePixmapCursor, which create a new cursor on each call. The Tk procedures are
also more portable than the lower-level X procedures.
The procedure Tk_NameOfCursor is roughly the inverse of Tk_GetCursor. If its cursor argument was created
by Tk_GetCursor, then the return value is the name argument that was passed to Tk_GetCursor to create the
cursor. If cursor was created by a call to Tk_GetCursorFromData, or by any other mechanism, then the
return value is a hexadecimal string giving the X identifier for the cursor. Note: the string returned
by Tk_NameOfCursor is only guaranteed to persist until the next call to Tk_NameOfCursor. Also, this call
is not portable except for cursors returned by Tk_GetCursor.
When a cursor returned by Tk_AllocCursorFromObj, Tk_GetCursor, or Tk_GetCursorFromData is no longer
needed, Tk_FreeCursorFromObj or Tk_FreeCursor should be called to release it. For Tk_FreeCursorFromObj
the cursor to release is specified with the same information used to create it; for Tk_FreeCursor the
cursor to release is specified with its Tk_Cursor token. There should be exactly one call to
Tk_FreeCursor for each call to Tk_AllocCursorFromObj, Tk_GetCursor, or Tk_GetCursorFromData.
BUGS
In determining whether an existing cursor can be used to satisfy a new request, Tk_AllocCursorFromObj,
Tk_GetCursor, and Tk_GetCursorFromData consider only the immediate values of their arguments. For
example, when a file name is passed to Tk_GetCursor, Tk_GetCursor will assume it is safe to re-use an
existing cursor 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. Similarly, Tk_GetCursorFromData assumes that if the same source pointer is used in two different
calls, then the pointers refer to the same data; it does not check to see if the actual data values have
changed.
KEYWORDS
cursor