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.
- const char *source (in)
- Data for cursor cursor, in standard cursor 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 cursor 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.
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
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
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 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 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 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
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
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_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
XCreateFontCursor 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_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
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