Fix PinchHandler.persistentTranslation; test cumulative native gestures

Since we do not want persistentTranslation to be always the same as
target.position, clearly we cannot use xAxis/yAxis to store the initial
target position: thus the startPos() function was wrong, and is now
removed. We need to store it in a separate m_startTargetPos variable
like DragHandler does, and as PinchHandler did before
7867a683fcb938939fb2837a26ac8e1941e3fe08.

Add an internal doc comment to clarify the arguments to
QQuickItemPrivate::adjustedPosForTransform().

tst_QQuickPinchHandler::cumulativeNativeGestures() now checks the result
of adjustedPosForTransform(): how far the target item moved.

Pick-to: 6.5
Fixes: QTBUG-111220
Change-Id: I04237cb82a1abaaeab873a0d887acaf322f262ce
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 20 insertions, 3 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index e745e4d110..ba161f5b27 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -5337,13 +5337,30 @@ bool QQuickItemPrivate::transformChanged(QQuickItem *transformedItem)
     return ret;
 }
 
+/*! \internal
+    Returns the new position (proposed values for the x and y properties)
+    to which this item should be moved to compensate for the given change
+    in scale from \a startScale to \a activeScale and in rotation from
+    \a startRotation to \a activeRotation. \a centroidParentPos is the
+    point that we wish to hold in place (and then apply \a activeTranslation to),
+    in this item's parent's coordinate system. \a startPos is this item's
+    position in its parent's coordinate system when the gesture began.
+    \a activeTranslation is the amount of translation that should be added to
+    the return value, i.e. the displacement by which the centroid is expected
+    to move.
+
+    If \a activeTranslation is \c (0, 0) the centroid is to be held in place.
+    If \a activeScale is \c 1, it means scale is intended to be held constant,
+    the same as \a startScale. If \a activeRotation is \c 0, it means rotation
+    is intended to be held constant, the same as \a startRotation.
+*/
 QPointF QQuickItemPrivate::adjustedPosForTransform(const QPointF &centroidParentPos,
                                                    const QPointF &startPos,
-                                                   const QVector2D &activeTranslation,  //[0,0] means no additional translation from startPos
+                                                   const QVector2D &activeTranslation,
                                                    qreal startScale,
-                                                   qreal activeScale,                   // 1.0 means no additional scale from startScale
+                                                   qreal activeScale,
                                                    qreal startRotation,
-                                                   qreal activeRotation)                // 0.0 means no additional rotation from startRotation
+                                                   qreal activeRotation)
 {
     Q_Q(QQuickItem);
     QVector3D xformOrigin(q->transformOriginPoint());