PinchHandler null target: remember accumulated scale between pinches

This restores behavior from b4d31c9ff5f0c5821ea127c663532d9fc2cae43e
which got broken in fc636af3a723ee8b4ee42cf71864ae0df5ca4621.
As documented, PinchHandler.scale is the accumulated scale that would
be applied to the target item (even if there is no target), whereas
activeScale is the scale during one pinch gesture. After the first
gesture, these two values are supposed to diverge, even if there is
no target; that way you can bind scale to some property, to scale
something else in the same way that PinchHandler would normally scale
its target.

Pick-to: 6.2 6.4
Fixes: QTBUG-108549
Task-number: QTBUG-68941
Task-number: QTBUG-92064
Change-Id: I32ff37e394fd8466128603eddd5697ba1cc1a0ed
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 50 insertions, 0 deletions

diff --git a/tests/manual/pointer/pinchNullTarget.qml b/tests/manual/pointer/pinchNullTarget.qml
new file mode 100644
index 0000000000..79c6047991
--- /dev/null
+++ b/tests/manual/pointer/pinchNullTarget.qml
@@ -0,0 +1,50 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick 2.15
+
+Rectangle {
+    width: 1024; height: 600
+    color: "#eee"
+
+    function getTransformationDetails(item, pinchhandler) {
+        return "\n\npinch.scale:" + pinchhandler.scale.toFixed(2)
+                + "\npinch.activeScale:" + pinchhandler.activeScale.toFixed(2)
+                + "\npinch.rotation:" + pinchhandler.rotation.toFixed(2)
+                + "\npinch.translation:" + "(" + pinchhandler.translation.x.toFixed(2) + "," + pinchhandler.translation.y.toFixed(2) + ")"
+                + "\nrect.scale: " + item.scale.toFixed(2)
+                + "\nrect.rotation: " + item.rotation.toFixed(2)
+                + "\nrect.position: " + "(" + item.x.toFixed(2) + "," + item.y.toFixed(2) + ")"
+    }
+
+    Rectangle {
+        width: parent.width - 100; height: parent.height - 100; x: 50; y: 50
+        color: "lightsteelblue"
+        antialiasing: true
+        scale: pinch.scale
+
+        PinchHandler {
+            id: pinch
+            target: null
+            minimumScale: 0.5
+            maximumScale: 3
+        }
+
+        Text {
+            text: "Pinch with 2 fingers to scale, rotate and translate"
+                  + getTransformationDetails(parent, pinch)
+        }
+    }
+
+    Rectangle {
+        id: centroidIndicator
+        x: pinch.centroid.scenePosition.x - radius
+        y: pinch.centroid.scenePosition.y - radius
+        z: 1
+        visible: pinch.active
+        radius: width / 2
+        width: 10
+        height: width
+        color: "red"
+    }
+}