Correct visible view calculations when using a wrapper element #38
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The previous expression (offset + wrapperTop) was only correct when the wrapped container was positioned at the top of the document. If the container was further down from the top of the document than the height of the last row, the last row would always be cloaked. The further down the container started, the more of the bottommost rows would always be cloaked. This was because "viewTop" was computed using document-relative coordinates, but was compared to a value (viewportBottom) that was clamped to the height of the container's content. This change uses a coordinate for viewTop which is relative to the scrolling container.
Incorporating wrapperTop into the calculated viewBottom shifts the computed bounds for all the views such that the first row is always found to be the topmost visible. Top put it another way, it prevents any of the views that scroll above the top from ever being cloaked when you're using a wrapper element.
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Both the find-top and find-bottom searches were incorrect (in different ways) for the case where you're scrolling the contents of one element (vs. the whole page). The details of the two problems are in the commit messages.
I believe that these changes will not affect the behavior in the full page scrolling case, but I have not tested that. (The change to find-top definitely will not affect full page scrolling — the value which is no longer added was always zero. The change to find-bottom effectively is substituting
position().topforoffset().top. I believe in the scrolling-the-whole-page case, these values are the same. In addition, the new find-bottom bounds computation now matches the find-top bounds computation, which further suggests to me that it's probably right.)