Before this change, we used Gfx::Bitmap to represent both decoded
images that are not going to be mutated and bitmaps corresponding
to canvases that could be mutated.
This change introduces a wrapper for bitmaps that are not going to be
mutated, so the painter could do caching: texture caching in the case
of GPU painter and potentially scaled bitmap caching in the case of CPU
painter.
Having two ways that `<position>` is represented is awkward and
unnecessary. So, let's combine the two paths together. This first step
copies and modifies the `parse_position()` code to produce a
`PositionStyleValue`.
Apart from returning a StyleValue, this also makes use of automatic enum
parsing instead of manually comparing identifier strings.
This modification introduces a new layer to the painting process. The
stacking context traversal no longer immediately calls the
Gfx::Painter methods. Instead, it writes serialized painting commands
into newly introduced RecordingPainter. Created list of commands is
executed later to produce resulting bitmap.
Producing painting command list will make it easier to add new
optimizations:
- It's simpler to check if the painting result is not visible in the
viewport at the command level rather than during stacking context
traversal.
- Run painting in a separate thread. The painting thread can process
serialized painting commands, while the main thread can work on the
next paintable tree and safely invalidate the previous one.
- As we consider GPU-accelerated painting support, it would be easier
to back each painting command rather than constructing an alternative
for the entire Gfx::Painter API.
Instead of resolving lengths used in the backdrop-filter during
painting, we can do that earlier in apply_style().
This change moves us a bit closer to the point when the stacking
context tree will be completely separated from the layout tree :)
Before this change, whenever ImageStyleValue had a non-null
`m_image_request`, it was always leaked along with everything related
to the document to which this value belongs. The issue arises due to
the use of `JS::Handle` for the image request, as it introduces a
cyclic dependency where `ImageRequest` prevents the `CSSStyleSheet`,
that owns `ImageStyleValue`, from being deallocated:
- ImageRequest
- FetchController
- FetchParams
- Window
- HTMLDocument
- HTMLHtmlElement
- HTMLBodyElement
- Text
- HTMLHeadElement
- Text
- HTMLMetaElement
- Text
- HTMLTitleElement
- Text
- HTMLStyleElement
- CSSStyleSheet
This change solves this by visiting `m_image_request` from
`visit_edges` instead of introducing new heap root by using
`JS::Handle`.
The `to_string()` for this is modified a little from the original,
because we have to calculate what the layer-count is then, instead of
having it already calculated.
In order to access the string's contents, use the new
`StringStyleValue::string_value()` method.
I think I found all the existing places that relied on
`StringStyleValue::to_string()` returning an unquoted string, but it's
hard to know for sure until things break.
This one is a bit fun because it can be `add(<integer>)` or `auto-add`,
but children have to inherit the computed value not the specified one.
We also have to compute it before computing the font-size, because of
`font-size: math` which will be implemented later.
Previously, the corner was always set to the top right, except if the
top left turned out to be closest, in which case it would be left
default-initialized instead.
Since we always pass the px value as an argument to resolved(), we can
pass it directly as CSSPixels instead of wrapping it in Length. This
approach allows us to avoid converting to a double, resulting in fewer
precision issues.
This is intended to annotate conversions from unknown floating-point
values to CSSPixels, and make it more obvious the fp value will be
rounded to the nearest fixed-point value.
In general it is not safe to convert any arbitrary floating-point value
to CSSPixels. CSSPixels has a resolution of 0.015625, which for small
values (e.g. scale factors between 0 and 1), can produce bad results
if converted to CSSPixels then scaled back up. In the worst case values
can underflow to zero and produce incorrect results.
The spec allows for these either to be based on the OS, or to be defined
by the browser. Looking at the other browser engines, there's a mix of
the two options. Since we've had issues with using OS colors as
defaults, let's use hard-coded colors for now. Some of these are based
on the definitions in
https://html.spec.whatwg.org/multipage/rendering.html
Reuse the check from IdentifierStyleValue in the CSS Parser, instead of
duplicating it. This might not be the ideal place to put it, but it
works for now.
