Tk_AllocCursorFromObj(3) Tk Library Procedures Tk_AllocCursorFromObj(3)______________________________________________________________________________NAME
Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj, Tk_GetCursor‐
FromData, Tk_NameOfCursor, Tk_FreeCursorFromObj, Tk_FreeCursor - main‐
tain 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 cursor; see below │
for possible values. Internal │
rep will be modified to cache │
pointer to corresponding Tk_Cur‐ │
sor. │
char *name (in) │
Same as objPtr except description │
of cursor is passed as a string │
and resulting Tk_Cursor isn't │
cached.
char *source (in) Data for cursor cursor, in stan‐
dard cursor format.
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 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.
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 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 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. Ap‐
pendix 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 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 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 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 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.
@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 │
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 stan‐
dard cursor data for the cursor's source bits, and mask points to stan‐
dard 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 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_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 XCreate‐
FontCursor 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_GetCursor‐ │
FromData.
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
Tk 8.1 Tk_AllocCursorFromObj(3)
