QGraphicsItem device coordinate cache unefficient in portrait mode

Problem was that we always invalidated the cache whenever the item was
rotated. This is however not required for simple rotations such as
90, 180 and 270 degrees. This commit also removes the somewhat arbitrary
logic which takes the desktop size into account. We now use the viewport
size instead.

Auto test included.

Task-number: QT-3779
Reviewed-by: yoann

1 files changed, 76 insertions, 0 deletions

diff --git a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
index 25ec040..2901dd5 100644
--- a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -445,6 +445,7 @@ private slots:
     void textItem_shortcuts();
     void scroll();
     void stopClickFocusPropagation();
+    void deviceCoordinateCache_simpleRotations();
 
     // task specific tests below me
     void task141694_textItemEnsureVisible();
@@ -10560,6 +10561,81 @@ void tst_QGraphicsItem::stopClickFocusPropagation()
     QVERIFY(itemWithFocus->hasFocus());
 }
 
+void tst_QGraphicsItem::deviceCoordinateCache_simpleRotations()
+{
+    // Make sure we don't invalidate the cache when applying simple
+    // (90, 180, 270, 360) rotation transforms to the item.
+    QGraphicsRectItem *item = new QGraphicsRectItem(0, 0, 300, 200);
+    item->setBrush(Qt::red);
+    item->setCacheMode(QGraphicsItem::DeviceCoordinateCache);
+
+    QGraphicsScene scene;
+    scene.setSceneRect(0, 0, 300, 200);
+    scene.addItem(item);
+
+    MyGraphicsView view(&scene);
+    view.show();
+    QTest::qWaitForWindowShown(&view);
+    QTRY_VERIFY(view.repaints > 0);
+
+    QGraphicsItemCache *itemCache = QGraphicsItemPrivate::get(item)->extraItemCache();
+    Q_ASSERT(itemCache);
+    QPixmapCache::Key currentKey = itemCache->deviceData.value(view.viewport()).key;
+
+    // Trigger an update and verify that the cache is unchanged.
+    QPixmapCache::Key oldKey = currentKey;
+    view.reset();
+    view.viewport()->update();
+    QTRY_VERIFY(view.repaints > 0);
+    currentKey = itemCache->deviceData.value(view.viewport()).key;
+    QCOMPARE(currentKey, oldKey);
+
+    // Check 90, 180, 270 and 360 degree rotations.
+    for (int angle = 90; angle <= 360; angle += 90) {
+        // Rotate item and verify that the cache was invalidated.
+        oldKey = currentKey;
+        view.reset();
+        QTransform transform;
+        transform.translate(150, 100);
+        transform.rotate(angle);
+        transform.translate(-150, -100);
+        item->setTransform(transform);
+        QTRY_VERIFY(view.repaints > 0);
+        currentKey = itemCache->deviceData.value(view.viewport()).key;
+        QVERIFY(currentKey != oldKey);
+
+        // IMPORTANT PART:
+        // Trigger an update and verify that the cache is unchanged.
+        oldKey = currentKey;
+        view.reset();
+        view.viewport()->update();
+        QTRY_VERIFY(view.repaints > 0);
+        currentKey = itemCache->deviceData.value(view.viewport()).key;
+        QCOMPARE(currentKey, oldKey);
+    }
+
+    // 45 degree rotation.
+    oldKey = currentKey;
+    view.reset();
+    QTransform transform;
+    transform.translate(150, 100);
+    transform.rotate(45);
+    transform.translate(-150, -100);
+    item->setTransform(transform);
+    QTRY_VERIFY(view.repaints > 0);
+    currentKey = itemCache->deviceData.value(view.viewport()).key;
+    QVERIFY(currentKey != oldKey);
+
+    // Trigger an update and verify that the cache was invalidated.
+    // We should always invalidate the cache for non-trivial transforms.
+    oldKey = currentKey;
+    view.reset();
+    view.viewport()->update();
+    QTRY_VERIFY(view.repaints > 0);
+    currentKey = itemCache->deviceData.value(view.viewport()).key;
+    QVERIFY(currentKey != oldKey);
+}
+
 void tst_QGraphicsItem::QTBUG_5418_textItemSetDefaultColor()
 {
     struct Item : public QGraphicsTextItem