UI|Client: Popups allow clicking through to widgets outside the popup

As a special case, mouse clicks on interactive widgets are allowed
to occur: even though the popup is open, it offers the event to
whichever widget is being hit even though the popup dismissal will
then eat the event and close the popup.

IssueID #1682

doomsday/client/src/ui/widgets/popupwidget.cpp

@@ -17,6 +17,7 @@
  */
 
 #include "ui/widgets/popupwidget.h"
+#include "ui/widgets/buttonwidget.h"
 #include "GuiRootWidget"
 #include "ui/style.h"
 #include "ui/clientwindow.h"
@@ -37,19 +38,21 @@ DENG_GUI_PIMPL(PopupWidget)
     bool useInfoStyle;
     bool deleteAfterDismiss;
     bool clickToClose;
+    bool outsideClickOngoing;
     Widget *realParent;
     Rule const *anchorX;
     Rule const *anchorY;
     Rule const *marker;
 
     Instance(Public *i)
-        : Base(i),
-          useInfoStyle(false),
-          deleteAfterDismiss(false),
-          clickToClose(true),
-          realParent(0),
-          anchorX(0),
-          anchorY(0)
+        : Base(i)
+        , useInfoStyle(false)
+        , deleteAfterDismiss(false)
+        , clickToClose(true)
+        , outsideClickOngoing(false)
+        , realParent(0)
+        , anchorX(0)
+        , anchorY(0)
     {
         // Style.
         marker = &style().rules().rule("gap");
@@ -250,12 +253,47 @@ bool PopupWidget::handleEvent(Event const &event)
         MouseEvent const &mouse = event.as<MouseEvent>();
         bool const inside = hitTest(event);
 
+        // Clicking outside the popup will close it.
         if(d->clickToClose)
         {
-            // Clicking outside the popup will close it.
-            if(!inside && mouse.state() == MouseEvent::Pressed)
+            switch(mouse.state())
             {
-                close(0); // immediately
+            case MouseEvent::Pressed:
+                if(!inside)
+                {
+                    d->outsideClickOngoing = true;
+                }
+                break;
+
+            case MouseEvent::Released:
+                if(!inside && d->outsideClickOngoing)
+                {
+                    /* This needs to satisfy the following conditions:
+                     *
+                     * - Since a mouse click comprises a Press followed by a Release, we shouldn't
+                     *   let the potential clicked widget that lies outside the popup know of the
+                     *   click before it has successfully completed.
+                     *
+                     * - Buttons perform their action when clicked, so the clicked widget must
+                     *   be notified before the popup is closed. This way buttons that open
+                     *   popup menus can either be used to toggle the menu open/closed, but also
+                     *   immediately open their menu if it currently is closed.
+                     */
+                    if(GuiWidget const *hit = root().globalHitTest(mouse.pos()))
+                    {
+                        if(hit->isEnabled() && hit->isVisible())
+                        {
+                            // Replay the click on this widget.
+                            const_cast<GuiWidget *>(hit)->handleEvent(
+                                    MouseEvent(mouse.button(), MouseEvent::Pressed, mouse.pos()));
+                            const_cast<GuiWidget *>(hit)->handleEvent(mouse);
+                        }
+                    }
+
+                    close(0); // immediately
+                }
+                d->outsideClickOngoing = false;
+                break;
             }
         }
         return true;