Tk_GetCursor(3) Tk (4.1) 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 cursor;
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.
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Tk_GetCursor(3) Tk (4.1) Tk_GetCursor(3)
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 previous call to
Tk_GetCursor or
Tk_GetCursorFromData.
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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 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 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 also supports all of the X
cursors. Tk on the Mac will also accept any of the
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Tk_GetCursor(3) Tk (4.1) Tk_GetCursor(3)
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 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 Macintosh or Windows
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). 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_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.
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Tk_GetCursor(3) Tk (4.1) Tk_GetCursor(3)
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 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_GetCursor or
Tk_GetCursorFromData. When a cursor is no longer in use
anywhere (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 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
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