From 47e38b7141a9e1ff3c93b37a2df24a8ae7d9781c Mon Sep 17 00:00:00 2001
From: David Edmundson <kde@davidedmundson.co.uk>
Date: Mon, 2 Aug 2021 00:11:27 +0100
Subject: [PATCH] Disconnect frame renders when ThumbnailItem has no window

It is perfectly valid to have a case where an item exists but has no
window. During these times the item will never be rendered.

Rather than guard in updateOffscreenTexture, it's more economical to
disable the frame rendering in the first place. Especially as then it's
easy to extend to item visibility.

BUG: 440318
---
 src/scripting/thumbnailitem.cpp | 18 ++++++++++++++----
 src/scripting/thumbnailitem.h   |  3 ++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/scripting/thumbnailitem.cpp b/src/scripting/thumbnailitem.cpp
index f272c2b16d..05687e6095 100644
--- a/src/scripting/thumbnailitem.cpp
+++ b/src/scripting/thumbnailitem.cpp
@@ -96,12 +96,14 @@ ThumbnailItemBase::ThumbnailItemBase(QQuickItem *parent)
     : QQuickItem(parent)
 {
     setFlag(ItemHasContents);
-    handleCompositingToggled();
+    updateFrameRenderingConnection();
 
     connect(Compositor::self(), &Compositor::aboutToToggleCompositing,
             this, &ThumbnailItemBase::destroyOffscreenTexture);
     connect(Compositor::self(), &Compositor::compositingToggled,
-            this, &ThumbnailItemBase::handleCompositingToggled);
+            this, &ThumbnailItemBase::updateFrameRenderingConnection);
+    connect(this, &QQuickItem::windowChanged,
+            this, &ThumbnailItemBase::updateFrameRenderingConnection);
 }
 
 ThumbnailItemBase::~ThumbnailItemBase()
@@ -143,14 +145,21 @@ QSGTextureProvider *ThumbnailItemBase::textureProvider() const
     return m_provider;
 }
 
-void ThumbnailItemBase::handleCompositingToggled()
+void ThumbnailItemBase::updateFrameRenderingConnection()
 {
+    disconnect(m_frameRenderingConnection);
+
     if (!Compositor::self()) {
         return;
     }
     Scene *scene = Compositor::self()->scene();
+
+    if (!window()) {
+        return;
+    }
+
     if (scene && scene->compositingType() == OpenGLCompositing) {
-        connect(scene, &Scene::frameRendered, this, &ThumbnailItemBase::updateOffscreenTexture);
+        m_frameRenderingConnection = connect(scene, &Scene::frameRendered, this, &ThumbnailItemBase::updateOffscreenTexture);
     }
 }
 
@@ -329,6 +338,7 @@ void WindowThumbnailItem::updateOffscreenTexture()
     if (m_acquireFence || !m_dirty || !m_client) {
         return;
     }
+    Q_ASSERT(window());
 
     const QRect geometry = m_client->frameGeometry();
     QSize textureSize = geometry.size();
diff --git a/src/scripting/thumbnailitem.h b/src/scripting/thumbnailitem.h
index 363d79341a..dfed036b5f 100644
--- a/src/scripting/thumbnailitem.h
+++ b/src/scripting/thumbnailitem.h
@@ -80,7 +80,8 @@ protected:
     qreal m_devicePixelRatio = 1;
 
 private:
-    void handleCompositingToggled();
+    void updateFrameRenderingConnection();
+    QMetaObject::Connection m_frameRenderingConnection;
 
     QSize m_sourceSize;
 };