NAME
Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj,
Tk_GetCursorFromData, Tk_NameOfCursor, Tk_FreeCursorFro
mObj, 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)
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 cur |
sor; see below for |
possible values. |
Internal rep will be |
modified to cache |
pointer to corre |
sponding Tk_Cursor. |
char *name (in) ||
Same as objPtr |
except description |
of cursor is passed |
as a string and |
resulting Tk_Cursor |
isn't cached.
sor, in standard
cursor format.
char *mask (in) Data for mask cur
sor, 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 allo
cated.
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_GetCursorFrom
Data.
_________________________________________________________________
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 describ |
ing 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 |
the return value in objPtr, which speeds up future calls |
to procedures such as Tk_AllocCursorFromObj and Tk_GetCur |
sorFromObj. 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 isn't 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 cur
sor cursor, i.e., any of the names defined in cur
sorcursor.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 speci
fied, they give the foreground and background col
ors to use for the cursor (any of the forms accept
able 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 Macin
tosh 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 cursors for the cursor's source
bits and mask. Each file must be in standard X11
or X10 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 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.
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 cur |
sor, given the window and description used to create the |
cursor. Tk_GetCursorFromObj doesn't 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). 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_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_GetCursorFrom
Data maintain a database of all the cursors they have cre
ated. 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
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 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_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_GetCursorFrom |
Data.
BUGS
In determining whether an existing cursor can be used to
satisfy a new request, Tk_AllocCursorFromObj, Tk_GetCur
sor, 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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