Introduce QGraphicsItem::ItemHasNoContents.

This flag helps optimize the case where an item is used only as a
transformation node in a scene graph, and where the item itself
doesn't paint anything. This is the default for FxItem (the
subclasses that do paint enable the HasContents flag). This lets
Graphics View know whether there's any point in setting up the
world transform, opacity and other things.

Reviewed-by: Lars

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 486e0b5..12aaba5 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -309,6 +309,11 @@
     and is always initialized to 1.
     Use QStyleOptionGraphicsItem::levelOfDetailFromTransform for a more
     fine-grained value.
+
+    \value ItemHasNoContents The item does not paint anything (i.e., calling
+    paint() on the item has no effect). You should set this flag on items that
+    do not need to be painted to ensure that Graphics View avoids unnecessary
+    painting preparations.
 */
 
 /*!
@@ -9108,6 +9113,9 @@ QDebug operator<<(QDebug debug, QGraphicsItem::GraphicsItemFlag flag)
     case QGraphicsItem::ItemUsesExtendedStyleOption:
         str = "ItemUsesExtendedStyleOption";
         break;
+    case QGraphicsItem::ItemHasNoContents:
+        str = "ItemHasNoContents";
+        break;
     }
     debug << str;
     return debug;