Tk_GetCursor(3) Tk Library Procedures Tk_GetCursor(3)______________________________________________________________________________NAME
Tk_GetCursor, Tk_GetCursorFromData, Tk_NameOfCursor, Tk_FreeCursor -
maintain database of cursors
SYNOPSIS
#include <tk.h>
Tk_Cursor
Tk_GetCursor(interp, tkwin, nameId)
Tk_Cursor
Tk_GetCursorFromData(interp, tkwin, source, mask, width, height, xHot, yHot, fg, bg)
char *
Tk_NameOfCursor(display, cursor)
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.
Tk_Uid nameId (in) Description of cursor; see below
for possible values.
char *source (in) Data for cursor bitmap, in stan‐
dard bitmap format.
char *mask (in) Data for mask bitmap, in standard
bitmap 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 toTk_FreeCursor, must
have been returned by some previ‐
ous call to Tk_GetCursor or
Tk_GetCursorFromData.
_________________________________________________________________DESCRIPTION
These procedures manage a collection of cursors being used by an appli‐
cation. The procedures allow cursors to be re-used efficiently,
thereby avoiding server overhead, and also allow cursors to be named
with character strings (actually Tk_Uids).
Tk_GetCursor takes as argument a Tk_Uid 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. NameId must be 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 font,
i.e., any of the names defined in cursorfont.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 illustra‐
tions 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 back‐
ground 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 also supports all of the X cursors.
Tk on the Mac will also accept any of the standard Mac cursors
including ibeam, crosshair, watch, plus, and arrow. In addi‐
tion, Tk will load Macintosh cursor resources of the types crsr
(color) and CURS (black and white) by the name of the 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 bitmaps for the cursor's source bits and mask. Each
file must be in standard X11 or X10 bitmap 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 Macin‐
tosh or Windows computers.
Tk_GetCursorFromData allows cursors to be created from in-memory
descriptions of their source and mask bitmaps. Source points to stan‐
dard bitmap data for the cursor's source bits, and mask points to stan‐
dard bitmap 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 includ‐
ing 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_GetCursor and Tk_GetCursorFromData will
return an identifier for the requested cursor. If an error occurs in
creating the cursor, such as when nameId refers to a non-existent file,
then None is returned and an error message will be stored in
interp->result.
Tk_GetCursor and Tk_GetCursorFromData maintain a database of all the
cursors they have created. Whenever possible, a call to Tk_GetCursor
or Tk_GetCursorFromData will return an existing cursor rather than cre‐
ating a new one. This approach can substantially reduce server over‐
head, 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 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 nameId 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_GetCursor or Tk_GetCursorFromData is no
longer needed, Tk_FreeCursor should be called to release it. There
should be exactly one call to Tk_FreeCursor for each call to Tk_GetCur‐
sor or Tk_GetCursorFromData. When a cursor is no longer in use any‐
where (i.e. it has been freed as many times as it has been gotten)
Tk_FreeCursor will release it to the X server and remove it from the
database.
BUGS
In determining whether an existing cursor can be used to satisfy a new
request, Tk_GetCursor and Tk_GetCursorFromData consider only the imme‐
diate 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
Tk 4.1 Tk_GetCursor(3)
