Destroy DecorationRenderer in setup/finish compositing

So far the DecorationRenderer got destroyed and recreated after
the signal compositing toggled was emitted. But that's too late for
e.g. the OpenGL Textures to be destroyed. So lets trigger the destroy
directly in setup/finish compositing. The new renderer will still be
created after the compositing toggled is emitted - we don't want to
have it recreated for the still active compositer type.

composite.cpp

@@ -39,6 +39,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #if HAVE_WAYLAND
 #include "wayland_backend.h"
 #endif
+#include "decorations/decoratedclient.h"
 
 #include <stdio.h>
 
@@ -1105,6 +1106,9 @@ bool Client::setupCompositing()
     if (!Toplevel::setupCompositing()){
         return false;
     }
+    if (decoratedClient()) {
+        decoratedClient()->destroyRenderer();
+    }
     updateVisibility(); // for internalKeep()
     return true;
 }
@@ -1114,7 +1118,9 @@ void Client::finishCompositing(ReleaseReason releaseReason)
     Toplevel::finishCompositing(releaseReason);
     updateVisibility();
     if (!deleting) {
-        triggerDecorationRepaint();
+        if (decoratedClient()) {
+            decoratedClient()->destroyRenderer();
+        }
     }
     // for safety in case KWin is just resizing the window
     s_haveResizeEffect = false;

decorations/decoratedclient.cpp

@@ -197,5 +197,11 @@ void DecoratedClientImpl::createRenderer()
     }
 }
 
+void DecoratedClientImpl::destroyRenderer()
+{
+    delete m_renderer;
+    m_renderer = nullptr;
+}
+
 }
 }

decorations/decoratedclient.h

@@ -81,6 +81,7 @@ public:
     Renderer *renderer() {
         return m_renderer;
     }
+    void destroyRenderer();
     KDecoration2::DecoratedClient *decoratedClient() {
         return KDecoration2::DecoratedClientPrivate::client();
     }