Fix performance regression in Image construction.

Setting up the signal leads to a significant memory and performance
overhead. This patch improves the benchmark by almost 10%.

Change-Id: Ib0a76ba42fdce1ca707044a8f8b6bdc6405f20c3
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

4 files changed, 9 insertions, 5 deletions

diff --git a/src/quick/items/qquickimage.cpp b/src/quick/items/qquickimage.cpp
index f0f17551b7..3ba09f9cea 100644
--- a/src/quick/items/qquickimage.cpp
+++ b/src/quick/items/qquickimage.cpp
@@ -152,7 +152,6 @@ QQuickImagePrivate::QQuickImagePrivate()
 QQuickImage::QQuickImage(QQuickItem *parent)
     : QQuickImageBase(*(new QQuickImagePrivate), parent)
 {
-    connect(this, SIGNAL(autoTransformBaseChanged()), SIGNAL(autoTransformChanged()));
 }
 
 QQuickImage::QQuickImage(QQuickImagePrivate &dd, QQuickItem *parent)
diff --git a/src/quick/items/qquickimage_p.h b/src/quick/items/qquickimage_p.h
index 5b1aea5940..8edf153ca3 100644
--- a/src/quick/items/qquickimage_p.h
+++ b/src/quick/items/qquickimage_p.h
@@ -88,6 +88,8 @@ public:
     bool mipmap() const;
     void setMipmap(bool use);
 
+    virtual void emitAutoTransformBaseChanged() { emit autoTransformChanged(); }
+
 Q_SIGNALS:
     void fillModeChanged();
     void paintedGeometryChanged();
diff --git a/src/quick/items/qquickimagebase.cpp b/src/quick/items/qquickimagebase.cpp
index 0e2134842b..223cb8f46f 100644
--- a/src/quick/items/qquickimagebase.cpp
+++ b/src/quick/items/qquickimagebase.cpp
@@ -197,7 +197,7 @@ void QQuickImageBase::load()
         }
         if (autoTransform() != d->oldAutoTransform) {
             d->oldAutoTransform = autoTransform();
-            emit autoTransformBaseChanged();
+            emitAutoTransformBaseChanged();
         }
         update();
 
@@ -284,7 +284,7 @@ void QQuickImageBase::requestFinished()
     }
     if (autoTransform() != d->oldAutoTransform) {
         d->oldAutoTransform = autoTransform();
-        emit autoTransformBaseChanged();
+        emitAutoTransformBaseChanged();
     }
     update();
 }
@@ -390,7 +390,7 @@ void QQuickImageBase::setAutoTransform(bool transform)
     if (d->autoTransform != UsePluginDefault && transform == (d->autoTransform == ApplyTransform))
         return;
     d->autoTransform = transform ? ApplyTransform : DoNotApplyTransform;
-    emit autoTransformBaseChanged();
+    emitAutoTransformBaseChanged();
 }
 
 QT_END_NAMESPACE
diff --git a/src/quick/items/qquickimagebase_p.h b/src/quick/items/qquickimagebase_p.h
index d43822bebe..4fcfaecd7d 100644
--- a/src/quick/items/qquickimagebase_p.h
+++ b/src/quick/items/qquickimagebase_p.h
@@ -83,6 +83,10 @@ public:
 
     void resolve2xLocalFile(const QUrl &url, qreal targetDevicePixelRatio, QUrl *sourceUrl, qreal *sourceDevicePixelRatio);
 
+    // Use a virtual rather than a signal->signal to avoid the huge
+    // connect/conneciton overhead for this rare case.
+    virtual void emitAutoTransformBaseChanged() { }
+
 Q_SIGNALS:
     void sourceChanged(const QUrl &);
     void sourceSizeChanged();
@@ -91,7 +95,6 @@ Q_SIGNALS:
     void asynchronousChanged();
     void cacheChanged();
     void mirrorChanged();
-    void autoTransformBaseChanged();
 
 protected:
     virtual void load();