qml: further limit miniplayer background effect source

modules/gui/qt/maininterface/qml/MainDisplay.qml

@@ -463,7 +463,12 @@ FocusScope {
                         stackView.forceActiveFocus()
                 }
 
-                effectSource: mainColumn
+                effectSource: stackView
+                effectSourceRect: effectSource.mapFromItem(parent,
+                                                           x,
+                                                           y,
+                                                           width,
+                                                           height)
             }
 
             Connections {

modules/gui/qt/player/qml/MiniPlayer.qml

@@ -34,6 +34,7 @@ FocusScope {
     visible: false
 
     property alias effectSource: effect.source
+    property alias effectSourceRect: effect.sourceRect
 
     state: (Player.playingState === Player.PLAYING_STATE_STOPPED) ? ""
                                                                   : "expanded"
@@ -70,11 +71,6 @@ FocusScope {
         id: effect
         anchors.fill: parent
 
-        sourceRect: Qt.rect(root.x,
-                            root.y,
-                            root.width,
-                            root.height)
-
         tint: VLCStyle.colors.lowerBanner
     }