STR #3424

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STR #3424

Application:FLTK Library
Status:1 - Closed w/Resolution
Priority:2 - Low, e.g. a documentation error or undocumented side-effect
Scope:2 - Specific to an operating system
Summary:X11: Fl_Window::default_cursor(FL_CURSOR_NONE) iterates
Created By:chris
Assigned To:manolo
Fix Version:1.4.0
Fix Commit:a47c907fca7b055f1f9428344d2dfefc36a9c9df
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Trouble Report Files:

Name/Time/Date Filename/Size top right image
#1 chris
23:41 May 25, 2020
bottom left image   bottom right image

Trouble Report Comments:

Name/Time/Date Text top right image
#1 chris
10:13 Nov 02, 2017
Discovered with a fresh build on a new X11 system with XCursor Library (libxcursor-dev) *not* installed and running some old code (for a touch screen system) that uses Fl_Window::default_cursor(FL_CURSOR_NONE) to hide the mouse cursor. The call runs into an endless loop and the application will be terminated after a while.

Can be tested with the cursor test program by e.g. adding a statement after line 33 in choice_cb:


and selecting FL_CURSOR_NONE.

(Before: compile FLTK with HAVE_XCURSOR 0 in config.h)

As fix I could find nothing better than (the program flow in fl_cursor.cxx is really hard to follow):

Index: src/fl_cursor.cxx
--- src/fl_cursor.cxx (Revision 12537)
+++ src/fl_cursor.cxx (Arbeitskopie)
@@ -172,7 +172,8 @@
   if (ret)
+  if (cursor_default != FL_CURSOR_NONE)
+    cursor(FL_CURSOR_DEFAULT);

#2 chris
04:50 May 06, 2020
It still happens with latest GIT version...
Seems an regression from FLTK 1.3, as it doesn't happen with the same code.

Is someone able to reproduce?
#3 chris
23:36 May 10, 2020
This is a regression from STR 2660:

Since then it is not possible to compile without using the xcursor library (HAVE_XCURSOR=0) and setting a window's default cursor to FL_CURSOR_NONE. Doing so will result in an endless loop and following stack overflow.
#4 chris
08:05 May 20, 2020
Some more analysis:

The code before the change did not use the XCursor library to define cursors, but used XCreatePixmapCursor or XCreateFontCursor.

The code after the change uses XcursorImageLoadCursor and as fallback if the XCursor library is not used (HAVE_CURSOR=0) it implements only the XCreateFontCursor method. But when the cursor type is not supported by XCreateFontCursor (e.g. FL_CURSOR_NONE, FL_CURSOR_NWSE,..) it comes to an endless loop. This is due the fact, that a failure of fallback_cursor() is not handled properly in fl_cursor.cxx.

The code to create a cursor from a Pixmap that was present in the original code has been removed completely, so there is no way to have that when not using the XCursor library.
#5 chris
23:40 May 25, 2020
I have re-added support for FL_CURSOR_NONE without dependeny on XCursor library, by using the relevant code parts that were removed by this commit:

Patch is attached.
#6 manolo
01:18 Nov 22, 2020
Fixed in Git repository.  
bottom left image   bottom right image

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