"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.
CSS defines a very specific paint order. This patch starts steering us
towards respecting that by introducing the PaintPhase enum with values:
- Background
- Border
- Foreground
- Overlay (internal overlays used by inspector)
Basically, to get the right visual result, we have to render the page
multiple times, going one phase at a time.
Fixed position elements have the ICB as their containing block.
The magic of fixed positioning is implemented at the rendering stage,
where we temporarily translate painting by the current scroll offset.
Note that "absolutely positioned" includes both position:absolute
and position:fixed.
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.
* A PageView is a view onto a Page object.
* A Page always has a main Frame (root of Frame tree.)
* Page has a PageClient. PageView is a PageClient.
The goal here is to allow building another kind of view onto
a Page while keeping the rest of LibWeb intact.
Now that PageView actually respects the invalidation rect provided by
the layout system, it turns out we were invalidating too little.
Unfortunately, this is not really fixable until the initial containing
block starts having the right size (same as viewport), but that will
require a bunch of work to make overflow work again. So it's a FIXME
for now, and we'll return to this.
When a paint invalidation occurs inside a subframe, it bubbles up to
Frame::set_needs_display(). From there, we call PageView if this is
the main frame, or otherwise invalidate the subframe host element.
You can still run the old parser with "br -O", but the new one is good
enough to be the default parser now. We'll fix issues as we go and
eventually remove the old one completely. :^)
