Previously, has_scrollable_overflow was a purely geometric check, true
whenever content extended beyond the padding box regardless of the
overflow property. This caused unnecessary scroll frame allocation for
boxes with `overflow:visible`.
Per CSS Overflow 3, scrollable overflow is only defined for scroll
containers (overflow: auto/hidden/scroll). Gate the flag on
`is_scroll_container()` so that only actual scroll containers get scroll
frames assigned.
Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
...with inline children. This fixes an issue when we ignore abspos boxes
contained by PaintableWithLines while calculating overflow rect size.
Lots of layout tests are affected, because now PaintableWithLines has
overflow rect.
`Text/input/DOM/Element-set-scroll-left.html` is also affected and now
matches other browsers.
Whenever we introduce a block element in a container that at that point
has only had inline children, we create an anonymous wrapper for all the
inline elements so we can keep the invariant that each container
contains either inline or non-inline children. For some reason, we
ignore all the out-of-flow nodes since they are layed out separately and
it was thought that this shouldn't matter.
However, if we are dealing with inline blocks and floating blocks, the
order of the inline contents _including_ out-of-flow nodes becomes very
important: floating blocks need to take the order of nodes into account
when positioning themselves.
Fix this by simply hoisting the out-of-flow nodes into the anonymous
wrapper as well.
Fixes the order of blocks in #4212. The gap is still not present.
Out-of-flow boxes (floating and absolutely-positioned elements) were
previously collected and put in the anonymous block wrapper as well, but
this actually made hit testing not able to find them, since they were
breaking expectations about tree structure that hit testing relies on.
After this change, we simply let out-of-flow boxes stay in their
original parent, preserving the author's intended box tree structure.
This patch just adds the new root paintable and updates the tests
expectations. The next patch will move painting logic from the layout
viewport to the paint viewport.
This patch does three things:
- Factors out the code that determines whether a box will create a new
formatting context for its children (and which type of context)
- Uses that code to mark all formatting context roots in layout tree
dumps. This makes it much easier to follow along with layout since
you can now see exactly where control is transferred to a new
formatting context.
- Rebaselines all existing layout tests, since the output format has
changed slightly.
