[webkit-dev] Table hit testing

Peter Kasting pkasting at google.com
Thu May 20 13:47:10 PDT 2010

On Thu, May 20, 2010 at 1:38 PM, David Hyatt <hyatt at apple.com> wrote:

> This is all coming back to me now.
> When two cells occupy the same position in the grid, only one of them gets
> stored at that position.  The current code puts the first cell encountered
> into the grid. This means if you ask what cell is present in row 3 and
> column 2 of the above example, you'll get back cell #5.
> This actually makes the grid unsuitable for hit testing and is why I hadn't
> converted nodeAtPoint over to use the grid yet.
> The grid needs to be fixed so that it records all of the cells present at a
> given position.  If it did that, then you could binary search as long as
> there are no overflowing cells, since you'd then be able to see all the
> cells that actually occupy a given grid position.
> The paint method uses the grid and actually has a repaint bug, since if you
> make the repaint rect tight enough, it won't think it has to paint the
> second and subsequent cells that occupy a given grid position.

It sounds like your recommended steps are:
* First fix the grid to record all the cells at a given position.  This
fixes a repaint bug.
* Then change the hit-testing to work just like painting.  This makes hit
testing more efficient and ensures hit testing and painting agree.
* Then optimize hit-testing to binary-search if there are no overflowing
cells.  (And optimize painting similarly?  I dunno what that would mean,
though--just going off the "optimize together" comment earlier.)

Is this a good summary?

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