[aurorae] do not make any blur calculations when blur is not supported

when an aurorae theme does not contain "mask" element we can safely assume that blur is not supported. In such case all blur calculations must not run at all. This will make all solid aurorae themes much lighter by default.

src/plugins/kdecorations/aurorae/src/aurorae.cpp

@@ -321,6 +321,9 @@ void Decoration::init()
         connect(m_view->contentItem(), &QQuickItem::heightChanged, m_item, updateSize);
         connect(m_view, &KWin::OffscreenQuickView::repaintNeeded, this, &Decoration::updateBuffer);
     }
+
+    m_supportsMask = m_item->property("supportsMask").toBool();
+
     setupBorders(m_item);
 
 
@@ -572,7 +575,7 @@ void Decoration::updateExtendedBorders()
 
 void Decoration::updateBlur()
 {
-    if (!m_item) {
+    if (!m_item || !m_supportsMask) {
         return;
     }
 

src/plugins/kdecorations/aurorae/src/aurorae.h

@@ -68,6 +68,8 @@ private:
     void updateBuffer();
     void updateExtendedBorders();
 
+    bool m_supportsMask{false};
+
     QRect m_contentRect; //the geometry of the part of the buffer that is not a shadow when buffer was created.
     QQuickItem *m_item = nullptr;
     QQmlContext *m_qmlContext = nullptr;

src/plugins/kdecorations/aurorae/src/qml/aurorae.qml

@@ -11,6 +11,7 @@ Decoration {
     id: root
     property bool animate: false
     property alias decorationMask: maskItem.mask
+    property alias supportsMask: backgroundSvg.supportsMask
     Component.onCompleted: {
         borders.left   = Qt.binding(function() { return Math.max(0, auroraeTheme.borderLeft);});
         borders.right  = Qt.binding(function() { return Math.max(0, auroraeTheme.borderRight);});
@@ -42,6 +43,7 @@ Decoration {
     }
     PlasmaCore.FrameSvg {
         property bool supportsInactive: hasElementPrefix("decoration-inactive")
+        property bool supportsMask: hasElementPrefix("mask")
         property bool supportsMaximized: hasElementPrefix("decoration-maximized")
         property bool supportsMaximizedInactive: hasElementPrefix("decoration-maximized-inactive")
         property bool supportsInnerBorder: hasElementPrefix("innerborder")