Tk_GetCursor(3)
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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 cur-
sor; see below for
possible values.
char *source (in) Data for cursor
bitmap, in standard
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 allo-
cated.
Tk_Cursor cursor (in) Opaque Tk identifier
for cursor. If
passed toTk_FreeCur-
sor, must have been
returned by some
previous call to
Tk_GetCursor or
Tk_GetCursorFrom-
Data.
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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
(actually Tk_Uids).
Tk_GetCursor takes as argument a Tk_Uid describing a cur-
sor, and returns an opaque Tk identifier for a cursor cor-
responding 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 follow-
ing forms:
name [fgColor [bgColor]]
Name is the name of a cursor in the standard X cur-
sor font, i.e., any of the names defined in cursor-
font.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 illus-
trations 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 spec-
ified, 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 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 addition, 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 con-
flicts color cursors will always be loaded in pref-
erence 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 com-
puters.
@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 Win-
dows computers.
Tk_GetCursorFromData allows cursors to be created from in-
memory descriptions of their source and mask bitmaps.
Source points to standard bitmap data for the cursor's
source bits, and mask points to standard 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). Typi-
cally, 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_GetCursor and Tk_GetCursor-
FromData will return an identifier for the requested cur-
sor. 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 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 XCre-
atePixmapCursor, 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 hex-
adecimal 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_NameOfCur-
sor. Also, this call is not portable except for cursors
returned by Tk_GetCursor.
When a cursor returned by Tk_GetCursor or Tk_GetCursor-
FromData 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_GetCursor or Tk_GetCur-
sorFromData. When a cursor is no longer in use anywhere
(i.e. it has been freed as many times as it has been got-
ten) 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_GetCursorFrom-
Data consider only the immediate values of their argu-
ments. 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