Fixed a bug where spans across empty cells got broken.

If a row/column is only used only because of the spanning of an item,
the cell should be treated as it didn't exist. We keep track of this
with the "ignore" bit array.

The old code would always start from the row/column at position 1.
In the attached testcase this made the effectiveRowSpan become larger
than actually needed.

Task-number: QTBUG-30255

Change-Id: Ief0e7018ee8e5ee36272ce075a43312ffeac7b91
(cherry picked from qtbase/f9e43c526a30ae3912adfe3d5cb781af5ddda4b0)
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

2 files changed, 29 insertions, 1 deletions

diff --git a/src/gui/graphicsview/qgridlayoutengine.cpp b/src/gui/graphicsview/qgridlayoutengine.cpp
index 8e6b149..99adb4a 100644
--- a/src/gui/graphicsview/qgridlayoutengine.cpp
+++ b/src/gui/graphicsview/qgridlayoutengine.cpp
@@ -1475,7 +1475,7 @@ void QGridLayoutEngine::fillRowData(QGridLayoutRowData *rowData, const QLayoutSt
 
                     int effectiveRowSpan = 1;
                     for (int i = 1; i < itemRowSpan; ++i) {
-                        if (!rowData->ignore.testBit(i))
+                        if (!rowData->ignore.testBit(i + itemRow))
                             ++effectiveRowSpan;
                     }
 
diff --git a/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp b/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
index d146b19..69291f5 100644
--- a/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
+++ b/tests/auto/qgraphicsgridlayout/tst_qgraphicsgridlayout.cpp
@@ -126,6 +126,7 @@ private slots:
     void spanningItem2x3_data();
     void spanningItem2x3();
     void spanningItem();
+    void spanAcrossEmptyRow();
     void heightForWidth();
     void widthForHeight();
     void heightForWidthWithSpanning();
@@ -3355,6 +3356,33 @@ void tst_QGraphicsGridLayout::spanningItem()
     QCOMPARE(layout->maximumSize(), QSizeF(160,80));
 }
 
+void tst_QGraphicsGridLayout::spanAcrossEmptyRow()
+{
+    QGraphicsWidget *form = new QGraphicsWidget(0, Qt::Window);
+    QGraphicsGridLayout *layout = new QGraphicsGridLayout(form);
+    layout->setContentsMargins(0, 0, 0, 0);
+    layout->setSpacing(0);
+    RectWidget *w1 = new RectWidget;
+    RectWidget *w2 = new RectWidget;
+    RectWidget *w3 = new RectWidget;
+
+    QSizeF size(10, 10);
+    for (int i = 0; i < 3; ++i) {
+        w1->setSizeHint((Qt::SizeHint)i, size);
+        w2->setSizeHint((Qt::SizeHint)i, size);
+        w3->setSizeHint((Qt::SizeHint)i, size);
+        size+=size;                 //[(10,10), (20,20), (40,40)]
+    }
+    layout->addItem(w1, 0, 0, 1, 1);
+    layout->addItem(w2, 0, 1, 1, 2);
+    layout->addItem(w3, 0, 99, 1, 1);
+
+    form->resize(60,20);
+    QCOMPARE(w1->geometry(), QRectF( 0, 0, 20, 20));
+    QCOMPARE(w2->geometry(), QRectF(20, 0, 20, 20));
+    QCOMPARE(w3->geometry(), QRectF(40, 0, 20, 20));
+}
+
 void tst_QGraphicsGridLayout::stretchAndHeightForWidth()
 {
     QGraphicsWidget *widget = new QGraphicsWidget(0, Qt::Window);