When decoding data into bitmaps, we end up with different alpha types
(premultiplied vs. unpremultiplied color data). Unfortunately, Skia only
seems to handle premultiplied color data well when scaling bitmaps with
an alpha channel. This might be due to Skia historically only supporting
premultiplied color blending, with unpremultiplied support having been
added more recently.
When using Skia to blend bitmaps, we need the color data to be
premultiplied. ImmutableBitmap gains a new method to enforce the alpha
type to be used, which is now used by SharedResourceRequest and
CanvasRenderingContext2D to enforce the right alpha type.
Our LibWeb tests actually had a couple of screenshot tests that exposed
the graphical glitches caused by Skia; see the big smiley faces in the
CSS backgrounds tests for example. The failing tests are now updated to
accommodate the new behavior.
Chromium and Firefox both seem to apply the same behavior; e.g. they
actively decode PNGs (which are unpremultiplied in nature) to a
premultiplied bitmap.
Fixes#3691.
Introduced in bd932858, the code would try to move `result.color_space`
into the ImmutableBitmap created for each single frame of an image. For
animated images, this would result in a use-after-move from the second
frame.
This patch introduces the `Gfx::ColorSpace` class, this is basically a
serializable wrapper for skia's SkColorSpace. Creation of the instances
of this class (and thus ICC profiles parsing) is performed in the
ImageDecoder process. Then the object is serialized and sent through
IPC, to finally be handed to skia for rendering.
However, to make sure that we're not making all LibGfx's users dependent
on Skia as well, we need to ensure the `Gfx::ColorSpace` object has no
dependency on objects from Skia. To that end, the only member of the
`ColorSpace` class is the opaque `ColorSpaceImpl` struct. Though, there
is on issue with that design, the code in `DisplayListPlayer.cpp` needs
access to the underlying `sk_sp<SkColorSpace>`. It is provided by a
template function, that is only specialized for this type.
Doing this work allows us to pass the following WPT tests:
- https://wpt.live/css/css-color/tagged-images-001.html
- https://wpt.live/css/css-color/tagged-images-003.html
- https://wpt.live/css/css-color/tagged-images-004.html
- https://wpt.live/css/css-color/untagged-images-001.html
Other test cases can also be found here:
- https://github.com/svgeesus/PNG-ICC-tests
Note that SkColorSpace support quite a limited amount of color spaces,
so color profiles like the ones in [1] or the v4 profiles in [2] are not
supported yet. In fact, SkColorSpace only accepts skcms_ICCProfile with
a linear conversion to XYZ D50.
[1] https://www.color.org/browsertest.xalter
[2] https://www.color.org/version4html.xalter
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
The main motivation behind this is to remove JS specifics of the Realm
from the implementation of the Heap.
As a side effect of this change, this is a bit nicer to read than the
previous approach, and in my opinion, also makes it a little more clear
that this method is specific to a JavaScript Realm.
