[webkit-dev] nodeAtPoint is very confusing

[Maciej Stachowiak]

On Apr 8, 2009, at 4:08 PM, David Hyatt wrote:

> Yeah this was on my list of things to do, but I stopped my big  
> render tree refactoring for the sake of stability.  I think we  
> should hold off on more big changes to render tree methods for now.

That is probably wise.

  - Maciej

>
> dave
>
> On Apr 8, 2009, at 5:50 PM, Maciej Stachowiak wrote:
>
>>
>> On Apr 8, 2009, at 9:23 AM, Simon Fraser wrote:
>>
>>> On Apr 8, 2009, at 7:06 AM, Eric Seidel wrote:
>>>
>>>> Dave, Simon, and other rendering gurus:
>>>>
>>>> bool RenderObject::nodeAtPoint(const HitTestRequest&,  
>>>> HitTestResult&
>>>> result, int _x, int _y, int tx, int ty, HitTestAction  
>>>> hitTestAction)
>>>>
>>>> _x, _y, tx, ty are very confusing.
>>>>
>>>> As far as I can tell, _x, _y are relative to the root layer  
>>>> (which can
>>>> change during hit-testing!) and tx, ty are more of the HTML  
>>>> "offset to
>>>> your parent" optimization which painting uses.
>>>>
>>>> Can you explain what the best way to convert from _x, _y to local
>>>> coordinates?  And what I should rename _x, _y, and tx, ty to in a
>>>> forthcoming "make hit testing readable to normal humans" cleanup
>>>> patch?
>>>
>>> As I understand it, _x and _y are relative to tx, ty, which in  
>>> turn is relative
>>> to the rootLayer.
>>>
>>> In general tx and ty, as passed to painting and hit testing  
>>> functions, are
>>> the offsets that put you in the coordinate space of the parent  
>>> renderer,
>>> relative to the current rootLayer  being used for painting or hit  
>>> testing
>>> (which, as you note, gets reset for transforms, and I think should
>>> also get reset for HTML/SVG boundaries).  So to get local x and y  
>>> for hit testing,
>>> you'll see code like:
>>>
>>> tx += x();
>>> ty += y()
>>> ...
>>> updateHitTestResult(_x - tx, _y - ty)
>>>
>>> It is all rather confusing, but much of the complexity comes from  
>>> having to
>>> deal with inlines.
>>
>> Maybe one thing that would help would be combining (tx, ty) into an  
>> IntPoint and (_x, _y) into an IntSize (since it as an offset from  
>> the point established by tx, ty). Or vice versa.
>>
>> Regards,
>> Maciej
>>
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>