Tk_AllocCursorFromObj(3tk)
Tk_AllocCursorFromObj(3Tk Library ProcedureTk_AllocCursorFromObj(3)
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NAME
Tk_AllocCursorFromObj, Tk_GetCursor, Tk_GetCursorFromObj,
Tk_GetCursorFromData, Tk_NameOfCursor, Tk_FreeCursorFromObj,
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)
const 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_Cursor.
char *name (in) Same as objPtr except
description of cursor
is passed as a string
and resulting
Tk_Cursor is not
cached.
Tk Last change: 8.1 1
Tk_AllocCursorFromObj(3Tk Library ProcedureTk_AllocCursorFromObj(3)
const char *source (in) Data for cursor cur-
sor, in standard cur-
sor format.
const 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 cur-
sor was allocated.
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_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.
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
Tk Last change: 8.1 2
Tk_AllocCursorFromObj(3Tk Library ProcedureTk_AllocCursorFromObj(3)
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 is
not 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. 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 tran-
sparent. 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 cur-
sors and will also accept any of the standard Mac cur-
sors 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 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 prefer-
ence 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 Macintosh or Windows comput-
ers.
@sourceName
Tk Last change: 8.1 3
Tk_AllocCursorFromObj(3Tk Library ProcedureTk_AllocCursorFromObj(3)
This form only works on Windows, and will load a Win-
dows system cursor (.ani or .cur) from the file speci-
fied 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 effi-
cient 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 does not 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 loca-
tion 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 argu-
ments 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 mes-
sage 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 over-
head, so the Tk procedures should generally be used in
preference to Xlib procedures like XCreateFontCursor or
Tk Last change: 8.1 4
Tk_AllocCursorFromObj(3Tk Library ProcedureTk_AllocCursorFromObj(3)
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_GetCursorFromData.
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 caus-
ing 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 Last change: 8.1 5
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