[webkit-dev] Why does PositionIterator iterates until the end of the document when selecting?

Ojan Vafai ojan at chromium.org
Thu Mar 29 13:56:37 PDT 2012

One case where this matters: <div

If you mousedown on foo and drag right, you want to start selecting bar. In
the common case, we don't do any walking. The next position we grab from
the iterator is valid and we use it.

On Thu, Mar 29, 2012 at 7:27 AM, Sergiy Byelozyorov <
byelozyorov at cs.uni-saarland.de> wrote:

> Hi,
> When searching for the character to be selected (on mouse click), we run
> an interator over the characters to determine the one under the cursor. I
> am trying to understand why does PositionInterator that is used in this
> case iterates over all characters starting from the element that was
> clicked and until the end of the document(!). The following method is
> called to verify whether PositionIterator has finished traversing the
> characters (see comments inline):
> bool PositionIterator::atEnd() const
> {
>     if (!m_anchorNode) // This is clear - if we don't have an an anchor -
> then we are done.
>         return true;
>     if (m_nodeAfterPositionInAnchor) // This is also understandable - if
> there is a next position then we are not at the end.
>         return false;
>     // This is what puzzles me. First check will be true until we will
> reach the root of the Document.
>     return !m_anchorNode->parentNode() && (m_anchorNode->hasChildNodes()
> || m_offsetInAnchor >= lastOffsetForEditing(m_anchorNode));
> }
> Is this the intended behaviour? Why wouldn't we just stay within the
> element that was clicked on? This would save us a lot of CPU cycles because
> we won't be checking text that in all other elements until the end of the
> document, wouldn't it? This check has been around since at least 2004, so I
> doub't that it's wrong, but I don't get the logic here. Please explain this
> to me. Thanks.
> Sergiy Byelozyorov
> Computer Graphics Chair
> Universitat des Saarlandes
> Tel.: +49 (681) 302-3837
> Web: http://graphics.cs.uni-saarland.de/sbyelozyorov/
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