Remove scene transform cache from QGraphicsItem.

Now that we have a recursive painting algorithm these types of
optimizations are no longer necessary. In fact they only cause more
problems and clutter up the code unnecessarily. Removing this also
removes extra overhead from moving and transforming items.

Reviewed-by: Lars

1 files changed, 8 insertions, 56 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 14658cf..c1848e0 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -918,9 +918,6 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent, bool de
     // Resolve depth.
     resolveDepth(parent ? parent->d_ptr->depth : -1);
 
-    // Invalidate transform cache.
-    invalidateSceneTransformCache();
-
     // Deliver post-change notification
     q->itemChange(QGraphicsItem::ItemParentHasChanged, newParentVariant);
 }
@@ -2526,7 +2523,6 @@ void QGraphicsItemPrivate::setPosHelper(const QPointF &pos)
     if (scene)
         q->prepareGeometryChange();
     this->pos = newPos;
-    invalidateSceneTransformCache();
 
     // Send post-notification.
     q->itemChange(QGraphicsItem::ItemPositionHasChanged, newPosVariant);
@@ -2667,44 +2663,15 @@ QMatrix QGraphicsItem::sceneMatrix() const
 */
 QTransform QGraphicsItem::sceneTransform() const
 {
-    // Check if there's any entry in the transform cache.
-    QGraphicsScenePrivate *sd = d_ptr->scene ? d_ptr->scene->d_func() : 0;
-    int index = d_ptr->sceneTransformIndex;
-    if (sd && index != -1 && sd->validTransforms.testBit(index))
-        return sd->sceneTransformCache[index];
-
-    // Calculate local transform.
     QTransform m;
-    if (d_ptr->hasTransform) {
-        m = transform();
-        if (!d_ptr->pos.isNull())
-            m *= QTransform::fromTranslate(d_ptr->pos.x(), d_ptr->pos.y());
-    } else if (!d_ptr->pos.isNull()) {
-        m = QTransform::fromTranslate(d_ptr->pos.x(), d_ptr->pos.y());
-    }
-
-    // Combine with parent and add to cache.
-    if (d_ptr->parent) {
-        m *= d_ptr->parent->sceneTransform();
-        // Don't cache toplevels
-        if (sd) {
-            if (index == -1) {
-                if (!sd->freeSceneTransformSlots.isEmpty()) {
-                    index = sd->freeSceneTransformSlots.last();
-                    sd->freeSceneTransformSlots.pop_back();
-                } else {
-                    index = sd->sceneTransformCache.size();
-                }
-                d_ptr->sceneTransformIndex = index;
-                if (index >= sd->validTransforms.size()) {
-                    sd->validTransforms.resize(index + 1);
-                    sd->sceneTransformCache.resize(index + 1);
-                }
-            }
-            sd->validTransforms.setBit(index, 1);
-            sd->sceneTransformCache[index] = m;
-        }
-    }
+    const QGraphicsItem *p = this;
+    do {
+        if (p->d_ptr->hasTransform)
+            m *= p->transform();
+        const QPointF &pos = p->d_ptr->pos;
+        if (!pos.isNull())
+            m *= QTransform::fromTranslate(pos.x(), pos.y());
+    } while ((p = p->d_ptr->parent));
     return m;
 }
 
@@ -2933,7 +2900,6 @@ void QGraphicsItem::setMatrix(const QMatrix &matrix, bool combine)
         d_ptr->transform = new QTransform(newTransform);
     else
         *d_ptr->transform = newTransform;
-    d_ptr->invalidateSceneTransformCache();
 
     // Send post-notification.
     // NB! We have to change the value from QMatrix to QTransform.
@@ -2982,7 +2948,6 @@ void QGraphicsItem::setTransform(const QTransform &matrix, bool combine)
         d_ptr->transform = new QTransform(newTransform);
     else
         *d_ptr->transform = newTransform;
-    d_ptr->invalidateSceneTransformCache();
 
     // Send post-notification.
     itemChange(ItemTransformHasChanged, newTransformVariant);
@@ -3912,19 +3877,6 @@ void QGraphicsItemPrivate::resolveDepth(int parentDepth)
 /*!
     \internal
 */
-void QGraphicsItemPrivate::invalidateSceneTransformCache()
-{
-    if (!scene || (parent && sceneTransformIndex == -1))
-        return;
-    if (sceneTransformIndex != -1)
-        scene->d_func()->validTransforms.setBit(sceneTransformIndex, 0);
-    for (int i = 0; i < children.size(); ++i)
-        children.at(i)->d_ptr->invalidateSceneTransformCache();
-}
-
-/*!
-    \internal
-*/
 void QGraphicsItemPrivate::addChild(QGraphicsItem *child)
 {
     child->d_ptr->siblingIndex = children.size();