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.
To make this possible, I also had to give each LayoutNode a Document&
so it can resolve document-specific colors correctly. There's probably
ways to avoid having this extra member by resolving colors later, but
this works for now.
"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.
We now implement the somewhat fuzzy shrink-to-fit algorithm when laying
out inline-block elements with both block and inline children.
Shrink-to-fit works by doing two speculative layouts of the entire
subtree inside the current block, to compute two things:
1. Preferred minimum width: If we made a line break at every chance we
had, how wide would the widest line be?
2. Preferred width: We break only when explicitly told to (e.g "<br>")
How wide would the widest line be?
We then shrink the width of the inline-block element to an appropriate
value based on the above, taking the available width in the containing
block into consideration (sans all the box model fluff.)
To make the speculative layouts possible, plumb a LayoutMode enum
throughout the layout system since it needs to be respected in various
places.
Note that this is quite hackish and I'm sure there are smarter ways to
do a lot of this. But it does kinda work! :^)
Add reasonable support for all values of white-space CSS property.
Values of the property are translated into a 3-tuple of rules:
do_collapse: whether whitespace is to be collapsed
do_wrap_lines: whether to wrap on word boundaries when
lines get too long
do_wrap_breaks: whether to wrap on linebreaks
The previously separate handling of per-line splitting and per-word
splitting have been unified. The Word structure is now a more
general Chunk, which represents different amounts of text depending
on splitting rules.
