Frames produced by block nodes are now always treated as exactly one per
given region and a frame must not be larger than its respective region.
Any overflow must be handled internally. This means that stack and grid
don't need to search for fitting regions anymore, since the child has
already does that for them. This commit further moves stack spacing into
a new `SpacingNode`.
The current inline alignment is very broken and leads to lots of subtle weirdness. Getting rid of it simplifies the stack's interface a lot. At a later point either:
- inline alignment will be added back in a better way, or
- all nodes will be able to expand or align themselves, meaning that the stack's children take care of their alignment
The previous paragraph layout algorithm had a couple of flaws:
- It always produced line break opportunities between runs although on
the textual level there might have been none.
- It didn't handle trailing spacing correctly in some cases.
- It wouldn't have been easily adaptable to Knuth-Plass style optimal
line breaking because it was fundamentally structured first-fit
run-by-run.
The new paragraph layout algorithm fixes these flaws. It proceeds
roughly in the following stages:
1. Collect all text in the paragraph.
2. Compute BiDi embedding levels.
3. Shape all runs, layout all children and store the resulting items in
a reusable (possibly even cacheable) `ParLayout`.
3. Iterate over all line breaks in the concatenated text.
4. Construct lightweight `LineLayout` objects for full lines instead of
runs. These mostly borrow from the `ParLayout` and only reshape the
first and last run if necessary. The design allows to use Harfbuzz's
UNSAFE_TO_BREAK mechanism to make reshaping more efficient. The size
of a `LineLayout` can be measured without building the line's frame.
5. Build only the selected line's frames and stack them.
- New naming scheme
- TextNode instead of NodeText
- CallExpr instead of ExprCall
- ...
- Less glob imports
- Removes Value::Args variant
- Removes prelude
- Renames Layouted to Fragment
- Moves font into env
- Moves shaping into layout
- Moves frame into separate module
This makes expansion behaviour inheritable by placing it into the area and passing it down during layouting instead of computing some approximation of what we want during execution.
