Boxes can now be floated left or right, which makes text within the
same block formatting context flow around them.
We were creating way too many block formatting contexts. As it turns
out, we don't need one for every new block, but rather there's a set
of rules that determines whether a given block creates a new block
formatting context.
Each BFC keeps track of the floating boxes within it, and IFC's can
then query it to find the available space for line boxes.
There's a huge hack in here where we assume all lines are the exact
line-height. Making this work with vertically non-uniform lines will
require some architectural changes.
We were not accounting for space occupied by borders when computing
the vertical (y) position of blocks. This meant that blocks with wide
top/bottom borders could bleed into each other incorrectly.
Fix this by using the combined padding+border geometry instead of just
the padding when placing blocks on the y axis.
We were incorrectly resolving relative length units (ex, em, etc.)
against the containing block in many cases. Fix this to resolve them
against the descendant box we're currently processing.
Bring the names of various boxes closer to spec language. This should
hopefully make things easier to understand and hack on. :^)
Some notable changes:
- LayoutNode -> Layout::Node
- LayoutBox -> Layout::Box
- LayoutBlock -> Layout::BlockBox
- LayoutReplaced -> Layout::ReplacedBox
- LayoutDocument -> Layout::InitialContainingBlockBox
- LayoutText -> Layout::TextNode
- LayoutInline -> Layout::InlineNode
Note that this is not strictly a "box tree" as we also hang inline/text
nodes in the same tree, and they don't generate boxes. (Instead, they
contribute line box fragments to their containing block!)
This is a first (huge) step towards modernizing the layout architecture
and bringing it closer to spec language.
Layout is now performed by a stack of formatting contexts, operating on
the box tree (or layout tree, if you will.)
There are currently three types of formatting context:
- BlockFormattingContext (BFC)
- InlineFormattingContext (IFC)
- TableFormattingContext (TFC)
Document::layout() creates the initial BlockFormattingContext (BFC)
which lays out the initial containing block (ICB), and then we recurse
through the tree, creating BFC, IFC or TFC as appropriate and handing
over control at the context boundaries.
The majority of this patch is just refactoring the old logic spread out
in LayoutBlock and LayoutTableRowGroup, and turning into these context
classes instead. A lot more cleanup will be needed.
There are many architectural wins here, the main one being that layout
is no longer performed by boxes themselves, which gives us much greater
flexibility in the outer/inner layout of a given box.
