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!)
Instead of computing it on the fly while painting each layout node,
they now remember their selection state. This avoids a whole bunch
of tree traversal while painting with anything selected.
We use this to ensure that we're always working with a selection where
the start() is before the end() in document order. That simplifies all
the logic around this.
Text selection currently works at the LayoutNode level. The root of the
layout tree has a LayoutRange selection() which in turn has two
LayoutPosition objects: start() and end().
A LayoutPosition is a LayoutNode + a text offset into that node.
We handle the selection painting in LayoutText::paint_fragment(), after
the normal painting is finished. The basic mechanism is that each
LayoutFragment is queried for its selection_rect(), and if a non-empty
rect is returned, we clip to it and paint the text once more.
"Paint" matches what we call this in the rest of the system. Let's not
confuse things by mixing paint/render/draw all the time. I'm guilty of
this in more places..
Also rename RenderingContext => PaintContext.
This kind of HTML now produces a single piece of whitespace:
<span> </span> <span> </span> <span> </span>
We achieve this by checking if the last fragment on the last line ends
in whitespace. If so, we either don't add a fragment at all (for the
current chunk) or we simply skip over all whitespace at the head of
the current chunk (instead of collapsing it to a single ' '.)
The box tree and line boxes now all store a relative offset from their
containing block, instead of an absolute (document-relative) position.
This removes a huge pain point from the layout system which was having
to adjust offsets recursively when something moved. It also makes some
layout logic significantly simpler.
Every box can still find its absolute position by walking its chain
of containing blocks and accumulating the translation from the root.
This is currently what we do both for rendering and hit testing.
