fixed DraggableControl not processing mouse events in some cases

It was possible for DraggableControls to return "processed = false"
for mouse events when it was being dragged very fast or when the mouse
leaves the screen while it was dragged. This should be fixed now.

Implementation note:
Nifty already supported exclusive mouse events for elements that are
focusable. When such an element was initially clicked the element
internally was marked as the one element that captured the mouse. Nifty
made sure that all mouse events were only sent to this element.

However it still was possible to have mouse events that didn't hit any
element at all and therefore were returned as "processed = false". This
has now been changed. Now all mouse events will be send to the element
that has captured the mouse no matter if the mouse hovers the element or
not.

Additionally when a DraggableControl is being dragged it is
now automatically marked as exclusive.

nifty-controls/src/main/java/de/lessvoid/nifty/controls/dragndrop/DraggableControl.java

@@ -142,6 +142,7 @@ private void moveDraggableToPopup() {
     draggable.markForMove(popup, new EndNotify() {
       @Override
       public void perform() {
+        draggable.getFocusHandler().requestExclusiveMouseFocus(draggable);
         draggable.setConstraintX(new SizeValue(originalPositionX + "px"));
         draggable.setConstraintY(new SizeValue(originalPositionY + "px"));
         draggable.getParent().layoutElements();

nifty-core/src/main/java/de/lessvoid/nifty/Nifty.java

@@ -1360,12 +1360,9 @@ private NiftyMouseInputEvent createEvent(final int mouseX, final int mouseY, fin
     }
 
     private boolean processEvent(final NiftyMouseInputEvent mouseInputEvent) {
-      boolean handled = false;
-      if (mouseInputEventProcessor.canProcess(mouseInputEvent)) {
-        mouseInputEventProcessor.process(mouseInputEvent);
-        handled = forwardMouseEventToScreen(mouseInputEvent);
-        handleDynamicElements();
-      }
+      mouseInputEventProcessor.process(mouseInputEvent);
+      boolean handled = forwardMouseEventToScreen(mouseInputEvent);
+      handleDynamicElements();
       pool.free(mouseInputEvent);
       return handled;
     }

nifty-core/src/main/java/de/lessvoid/nifty/controls/FocusHandler.java

@@ -312,6 +312,10 @@ public boolean hasAnyElementTheKeyboardFocus() {
     return keyboardFocusElement != null;
   }
 
+  public boolean hasAnyElementTheMouseFocus() {
+    return mouseFocusElement != null;
+  }
+
   public Element findElement(final String defaultFocusElementId) {
     for (Element element : entries) {
       if (defaultFocusElementId.equals(element.getId())) {

nifty-core/src/main/java/de/lessvoid/nifty/input/mouse/MouseInputEventProcessor.java

@@ -26,29 +26,8 @@ public void begin() {
     hadAnyEvents = false;
   }
 
-  public boolean canProcess(final NiftyMouseInputEvent mouseEvent) {
-    hadAnyEvents = true;
-
-    int mouseX = mouseEvent.getMouseX();
-    int mouseY = mouseEvent.getMouseY();
-    int mouseWheel = mouseEvent.getMouseWheel();
-    boolean button0Down = mouseEvent.isButton0Down();
-    boolean button1Down = mouseEvent.isButton1Down();
-    boolean button2Down = mouseEvent.isButton2Down();
-
-    if (mouseX != lastMouseX ||
-        mouseY != lastMouseY ||
-        mouseWheel != 0 ||
-        button0Down != lastButtonDown0 ||
-        button1Down != lastButtonDown1 ||
-        button2Down != lastButtonDown2) {
-      return true;
-    }
-
-    return false;
-  }
-
   public void process(final NiftyMouseInputEvent mouse) {
+    hadAnyEvents = true;
     mouse.setButton0InitialDown(!lastButtonDown0 && mouse.isButton0Down());
     mouse.setButton0Release(lastButtonDown0 && !mouse.isButton0Down());
     mouse.setButton1InitialDown(!lastButtonDown1 && mouse.isButton1Down());

nifty-core/src/main/java/de/lessvoid/nifty/screen/Screen.java

@@ -347,9 +347,15 @@ private boolean forwardMouseEventToLayers(final List < Element > layerList, fina
     mouseOverHandler.reset();
 
     long eventTime = timeProvider.getMsTime();
-    for (int i=0; i<layerList.size(); i++) {
-      Element layer = layerList.get(i);
-      layer.buildMouseOverElements(inputEvent, eventTime, mouseOverHandler);
+
+    if (focusHandler.hasAnyElementTheMouseFocus()) {
+      Element e = focusHandler.getMouseFocusElement();
+      mouseOverHandler.addMouseOverElement(e);
+    } else {
+      for (int i=0; i<layerList.size(); i++) {
+        Element layer = layerList.get(i);
+        layer.buildMouseOverElements(inputEvent, eventTime, mouseOverHandler);
+      }
     }
 
     if (log.isLoggable(Level.FINER)) {