Redraw issues when removing a fully transparent QGraphicsItem from the scene.

This only happened with fully transparent ancestors (item's
effectiveOpacity() == 0.0). Problem was that we didn't take into
account the ancestors' opacity when removing an item from the scene.
More specifically: The calculated effective opacity for the item was
zero and we ignored update requests. We have to ignore the opacity if
any of the ancestors' ignoreOpacity bit is 1, which means the opacity
is set to 0 and the update request has not yet been processed.

Auto test included.

Task-number: QTBUG-10778

1 files changed, 18 insertions, 0 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index ae0abf9..22c3f92 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -4889,6 +4889,24 @@ void QGraphicsScenePrivate::markDirty(QGraphicsItem *item, const QRectF &rect, b
     if (updateAll)
         return;
 
+    if (removingItemFromScene && !ignoreOpacity && !item->d_ptr->ignoreOpacity) {
+        // If any of the item's ancestors ignore opacity, it means that the opacity
+        // was set to 0 (and the update request has not yet been processed). That
+        // also means that we have to ignore the opacity for the item itself; otherwise
+        // things like: parent->setOpacity(0); scene->removeItem(child) won't work.
+        // Note that we only do this when removing items from the scene. In all other
+        // cases the ignoreOpacity bit propagates properly in processDirtyItems, but
+        // since the item is removed immediately it won't be processed there.
+        QGraphicsItem *p = item->d_ptr->parent;
+        while (p) {
+            if (p->d_ptr->ignoreOpacity) {
+                item->d_ptr->ignoreOpacity = true;
+                break;
+            }
+            p = p->d_ptr->parent;
+        }
+    }
+
     if (item->d_ptr->discardUpdateRequest(/*ignoreVisibleBit=*/force,
                                           /*ignoreDirtyBit=*/removingItemFromScene || invalidateChildren,
                                           /*ignoreOpacity=*/ignoreOpacity)) {