Keep sending FL_DRAG until all mouse buttons are released

The old version would send FL_MOVE events after dragging with more
than one mouse buttons pressed, as soon as the first button was
released.

The new version sends FL_DRAG until the last mouse button is released
and then FL_MOVE, as usual.

This change affects dragging only if more than one mouse button is
pushed and held while dragging. The order of pushing and releasing
mouse buttons does not affect the behavior.

1 files changed, 32 insertions, 7 deletions

diff --git a/src/Fl.cxx b/src/Fl.cxx
index f1ad4d75c..429c5c74a 100644
--- a/src/Fl.cxx
+++ b/src/Fl.cxx
@@ -1359,7 +1359,7 @@ int Fl::handle_(int e, Fl_Window* window)
       ret = (wi && send_event(e, wi, window));
       if (pbm != belowmouse()) {
 #ifdef DEBUG
-        printf("Fl::handle(e=%d, window=%p);\n", e, window);
+        printf("Fl::handle(e=%d, window=%p) -- Fl_Tooltip::enter(%p);\n", e, window, belowmouse());
 #endif // DEBUG
         Fl_Tooltip::enter(belowmouse());
       }
@@ -1367,19 +1367,44 @@ int Fl::handle_(int e, Fl_Window* window)
     }
 
   case FL_RELEASE: {
-//    printf("FL_RELEASE: window=%p, pushed() = %p, grab() = %p, modal() = %p\n",
-//           window, pushed(), grab(), modal());
+
+    // Mouse drag release mode - Jul 14, 2023, Albrecht-S (WIP):
+    //   0 = old: *first* mouse button release ("up") turns drag mode off
+    //   1 = new: *last* mouse button release ("up") turns drag mode off
+    // The latter enables dragging with two or more pressed mouse buttons
+    // and to continue dragging (i.e. sending FL_DRAG) until the *last*
+    // mouse button is released.
+    // See fltk.general, thread started on Jul 12, 2023
+    // "Is handling simultaneous Left-click and Right-click drags supported?"
+
+    static const int drag_release = 1; // should be 1 => new behavior since Jul 2023
+
+    // Implementation notes:
+    // (1) Mode 1 (new): only if *all* mouse buttons have been released, the
+    //     Fl::pushed_ widget is reset to 0 (NULL) so subsequent system "move"
+    //     events are no longer sent as FL_DRAG events.
+    // (2) Mode 0 (old): Fl::pushed_ was reset on the *first* mouse button release.
+    // (3) The constant 'drag_release' should be removed once the new mode has been
+    //     confirmed to work correctly and no side effects have been observed.
+    //     Hint: remove condition "!drag_release || " twice (below).
+
+    // printf("FL_RELEASE: window=%p, pushed() = %p, grab() = %p, modal() = %p, drag_release = %d, buttons = 0x%x\n",
+    //        window, pushed(), grab(), modal(), drag_release, Fl::event_buttons()>>24);
 
     if (grab()) {
       wi = grab();
-      pushed_ = 0; // must be zero before callback is done!
+      if (!drag_release || !Fl::event_buttons())
+        pushed_ = 0; // must be zero before callback is done!
     } else if (pushed()) {
       wi = pushed();
-      pushed_ = 0; // must be zero before callback is done!
-    } else if (modal() && wi != modal()) return 0;
+      if (!drag_release || !Fl::event_buttons())
+        pushed_ = 0; // must be zero before callback is done!
+    } else if (modal() && wi != modal())
+      return 0;
     int r = send_event(e, wi, window);
     fl_fix_focus();
-    return r;}
+    return r;
+  }
 
   case FL_UNFOCUS:
     window = 0;