directly scale the content item when pinching

when pinching, just scale the item, this scales the texture
with the GPU, avoiding costrly redraws.
redraw at the correct size only when the gesture ends

mobile/components/DocumentView.qml

@@ -32,8 +32,12 @@ QtControls.ScrollView {
     id: root
     property DocumentItem document
     property PageItem page: mouseArea.currPageDelegate.pageItem
+
+    onWidthChanged: resizeTimer.restart()
+    onHeightChanged: resizeTimer.restart()
     Flickable {
         id: flick
+        anchors.fill: parent
         
         clip: true
 
@@ -41,8 +45,6 @@ QtControls.ScrollView {
             flick.contentWidth = flick.width
             flick.contentHeight = flick.width / mouseArea.currPageDelegate.pageRatio
         }
-        onWidthChanged: resizeTimer.restart()
-        onHeightChanged: resizeTimer.restart()
         Connections {
             target: root.document
             onPathChanged: resizeTimer.restart()
@@ -74,7 +76,17 @@ QtControls.ScrollView {
                 flick.contentY += pinch.previousCenter.y - pinch.center.y
 
                 // resize content
-                flick.resizeContent(Math.max(flick.width+1, initialWidth * pinch.scale), Math.max(flick.height, initialHeight * pinch.scale), pinch.center);
+                //use the scale property during pinch, for speed reasons
+                if (initialHeight * pinch.scale > flick.height &&
+                    initialHeight * pinch.scale < flick.height * 3) {
+                    mouseArea.scale = pinch.scale;
+                }
+                flick.returnToBounds();
+            }
+            onPinchFinished: {
+                flick.resizeContent(Math.max(flick.width+1, initialWidth * mouseArea.scale), Math.max(flick.height, initialHeight * mouseArea.scale), pinch.center);
+                mouseArea.scale = 1;
+
                 flick.returnToBounds();
             }
             MouseArea {