tdf#156473 a11y: Don't use selection index as child index

`XAccessibleSelection::getSelectedAccessibleChild` takes
the index into the selection, not the child index, as its
documentation (in
`offapi/com/sun/star/accessibility/XAccessibleSelection.idl`)
says:

> @param nSelectedChildIndex
>     This index refers only to the selected children, not to all the
>     children of this object.  Even if all children are selected, the
>     indices enumerating the selected children need not be the same
>     as those enumerating all children.  If only single selection is
>     supported the only valid value is 0.

The previous handling here in
`AccessibleGridControlTable::getSelectedAccessibleChild`
was treating it as the child index, though. Therefore
trying to get the selected children would break once
any row other than the first was selected.

Fix this by calculating the actual row/column index
of the cell from the given *selection* index.

This could be observed e.g. with the qt6 VCL plugin by
querying selection from Accerciser, with the last row
selected in the table from the tdf#156473 macro in LO
and the corresponding table object selected in
Accerciser's tree view of the LO a11y hierarchy:

Before:

In [41]: sel = acc.querySelection()
In [42]: sel.nSelectedChildren
Out[42]: 5
In [43]: sel.getSelectedChild(0)
In [44]: sel.getSelectedChild(0) == None
Out[44]: True

With the fix in place:

In [48]: sel = acc.querySelection()
In [49]: sel.nSelectedChildren
Out[49]: 5
In [50]: sel.getSelectedChild(0)
Out[50]: <Atspi.Accessible object at 0x7fcaeaddb900 (AtspiAccessible at 0x3ae4a80)>
In [51]: sel.getSelectedChild(0).name
Out[51]: 'C1 , R4 , '
In [52]: sel.getSelectedChild(1).name
Out[52]: 'C2 , R4 , '
In [53]: sel.getSelectedChild(4).name
Out[53]: 'Column 5 , R4 , '

Change-Id: Id7d42a89b913d2ed101a9edb45dee5f3d870dbbd
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/155190
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

1 files changed, 10 insertions, 4 deletions

diff --git a/accessibility/source/extended/AccessibleGridControlTable.cxx b/accessibility/source/extended/AccessibleGridControlTable.cxx
index 579826195be2..4629a4b3ee66 100644
--- a/accessibility/source/extended/AccessibleGridControlTable.cxx
+++ b/accessibility/source/extended/AccessibleGridControlTable.cxx
@@ -253,10 +253,16 @@ AccessibleGridControlTable::getSelectedAccessibleChild( sal_Int64 nSelectedChild
     SolarMutexGuard aSolarGuard;
 
     ensureIsAlive();
-    if(isAccessibleChildSelected(nSelectedChildIndex))
-        return getAccessibleChild(nSelectedChildIndex);
-    else
-        return nullptr;
+    if (nSelectedChildIndex < 0 || nSelectedChildIndex >= getSelectedAccessibleChildCount())
+        throw lang::IndexOutOfBoundsException("Invalid index into selection", *this);
+
+    const sal_Int32 nColCount = getAccessibleColumnCount();
+    assert(nColCount > 0 && "Column count non-positive, but child count > 0");
+    const sal_Int32 nIndexInSelectedRowsSequence = nSelectedChildIndex / nColCount;
+    const Sequence<sal_Int32> aSelectedRows = getSelectedAccessibleRows();
+    const sal_Int32 nRowIndex = aSelectedRows[nIndexInSelectedRowsSequence];
+    const sal_Int32 nColIndex = nSelectedChildIndex % nColCount;
+    return getAccessibleCellAt(nRowIndex, nColIndex);
 }
 //not implemented yet, because only row selection possible
 void SAL_CALL AccessibleGridControlTable::deselectAccessibleChild(