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ActiveTcl User Guide |  |
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ActiveTcl User Guide | |
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:
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.
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 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.
Copyright © 1990 The Regents of the University of California. Copyright © 1994-1998 Sun Microsystems, Inc. Copyright © 1995-1997 Roger E. Critchlow Jr.