SwipeView: position the pages adjacent to each other initially

ListView only manages the positions of the visible delegates; but the
children of SwipeView are instantiated at startup. When we didn't set
their positions, if they are translucent, they were simply piled up
on top of each other until ListView got around to positioning them
during swiping. Between a055629f43cf8589ff6d69e46b2610429aaa4167 and
e10de033f4c44855de7287a97e2aa651f648742e SwipeView was calling
setCulled(true); we stopped doing that because of QTBUG-99547.
So now it makes sense to position the delegates the same way that
ListView will eventually position them... assuming there are no
other special cases for custom positioning. They are still
effectively "culled" by being outside the viewport, or the clip.

Fixes: QTBUG-102487
Task-number: QTBUG-51078
Task-number: QTBUG-51669
Task-number: QTBUG-99547
Change-Id: I58afab55cc95a1d4a637111a9cca82e6177856ff
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
(cherry picked from commit 7a5bbc23150fe73f86e9eb81d252cb8ebc673784)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 32 insertions, 3 deletions

diff --git a/src/quicktemplates2/qquickswipeview.cpp b/src/quicktemplates2/qquickswipeview.cpp
index e41b328477..18d04d5724 100644
--- a/src/quicktemplates2/qquickswipeview.cpp
+++ b/src/quicktemplates2/qquickswipeview.cpp
@@ -158,11 +158,10 @@ void QQuickSwipeViewPrivate::resizeItems()
                 qmlWarning(item) << "SwipeView has detected conflicting anchors. Unable to layout the item.";
                 item->setProperty("_q_QQuickSwipeView_warned", true);
             }
-
             if (orientation == Qt::Horizontal)
-                item->setY(0);
+                item->setPosition({i * (contentItem->width() + spacing), 0});
             else
-                item->setX(0);
+                item->setPosition({0, i * (contentItem->height() + spacing)});
             item->setSize(QSizeF(contentItem->width(), contentItem->height()));
         }
     }
diff --git a/tests/auto/quickcontrols2/controls/data/tst_swipeview.qml b/tests/auto/quickcontrols2/controls/data/tst_swipeview.qml
index c9629de906..254c876f08 100644
--- a/tests/auto/quickcontrols2/controls/data/tst_swipeview.qml
+++ b/tests/auto/quickcontrols2/controls/data/tst_swipeview.qml
@@ -686,4 +686,34 @@ TestCase {
         var image = grabImage(control)
         compare(image.pixel(3, 3), "#ffff00")
     }
+
+    Component {
+        id: translucentPages
+        SwipeView {
+            spacing: 10
+            padding: 10
+            Text { text: "page 0" }
+            Text { text: "page 1"; font.pointSize: 16 }
+            Text { text: "page 2"; font.pointSize: 24 }
+            Text { text: "page 3"; font.pointSize: 32 }
+        }
+    }
+
+    function test_initialPositions() { // QTBUG-102487
+        const control = createTemporaryObject(translucentPages, testCase, {width: 320, height: 200})
+        verify(control)
+        compare(control.orientation, Qt.Horizontal)
+        for (var i = 0; i < control.count; ++i) {
+            const page = control.itemAt(i)
+            // control.contentItem.width + control.spacing == 310; except Imagine style has contentItem.width == 320
+            compare(page.x, i * 310)
+            compare(page.y, 0)
+        }
+        control.orientation = Qt.Vertical
+        for (var i = 0; i < control.count; ++i) {
+            const page = control.itemAt(i)
+            compare(page.y, i * (control.contentItem.height + control.spacing))
+            compare(page.x, 0)
+        }
+    }
 }