Previously animation ownership was a messy split between
`AnimatedBitmapDecodedImageData` and the consumers (i.e.
`ImageStyleValueResource`, `HTMLImageElement`, and `SVGImageElement`)
with `AnimatedBitmapDecodedImageData` owning the frames and a current
frame index, and the consumers owning the rest of the state (e.g. loop
count, timers to drive the animation forward, their own current index).
This had a couple of main issues:
- While `AnimatedDecodedImageData` partially synchronized animations by
dropping unexpected advancement notifications, this didn't apply to
other animation state which meant, for instance, that a later started
consumer could drive the animation of an earlier one past the max
loop count (albeit without invalidating the earlier consumer).
- Multiple consumers didn't share frame timings, meaning animations
could be up to a full frame out of sync visually.
- Animations were paused depending on whether there were any consumers,
this is different to the behavior in other browsers (where they
continue regardless of whether there are any consumers).
- It was an overgeneralization of how animations need to work - only
`AnimatedBitmapDecodedImageData` works with an indexed frame model,
with animated SVGs (although not yet implemented) relying on their
internal event loop to be driven forward.
Given the above the new approach implemented in this commit is:
- The API for `DecodedImageData` is animation system agnostic, only
exposing `default_frame`, `current_frame`, and `restart_animation`
methods not reliant on providing a specific frame index.
- `AnimatedBitmapDecodedImageData` owns its own timer, loop count,
etc. The animation starts when the first consumer registers and ends
when the document is hidden or becomes inactive (or completes in the
case of finite animations).
- Consumers are invalidated by `AnimatedBitmapDecodedImageData` when
required.
Tests have been added for:
- Animations being paused when the document becomes inactive and
restarted when it becomes active again.
- Frame timings being synchronized across consumers.
- Restarts triggered by `HTMLImageElement` applying to all consumers.
- Processing ending once a non-infinite animation plays to completion.
The tests to ensure animations are cancelled when consumers are removed
(e.g. `animated-background-image-timer-stops-when-hidden.html`) have
been updated to assert the inverse since animation state is now per
resource not per consumer.
This allows us to remove the `frame_rect` accessor.
This also fixes a bug where we computed the scaling mode based on the
clipping rect rather than the draw rect for `ImagePaintable`
DecodedImageData::paint() used to take both a destination and a
clip rectangle even though most callers passed the same value. SVG
image painting used that API to wrap every nested SVG display list in
save/add-clip/restore, which put an unbounded command in front of
the bounded nested-list command and made offscreen SVG image content
harder to cull.
Move clipping to ImagePaintable, where the object-fit destination can
be compared with the replaced element box. CSS image and marker
painting continue to draw into their destination rect, while repeated
background images keep their explicit tile clip. The scaled decoded
image display-list command now stores only its destination rect and
uses that as its bounds; playback still clips decoded images to that
rect so bitmap rendering stays unchanged.
DecodedImageFrame only wraps a ref-counted Bitmap and color-space
metadata. The frame object itself does not provide shared mutable
state or lifetime ownership beyond those members, so ref-counting it
adds an unnecessary layer of indirection.
Report DOM character data, decoded image frames, ImageBitmap pixel
buffers, and 2D canvas surfaces through the GC external memory hook.
This lets image and text-heavy pages participate in GC threshold
calculations through their retained backing storage.
Decoded image data should not continue to traffic in ImmutableBitmap now
that the bitmap wrapper is being retired. Introduce DecodedImageFrame as
the paintable decoded-image unit and store a Bitmap plus ColorSpace in
it directly.
Thread the new frame type through decoded image data, display-list
image commands, filters, canvas drawImage, patterns, WebGL texture
upload, and CSS/SVG image consumers. ImmutableBitmap remains only at
the legacy boundaries that still need it, such as HTML video snapshots
and callers that explicitly ask for a bitmap snapshot.
This keeps color-space ownership with the decoded frame while making
the expensive or legacy ImmutableBitmap path explicit at the few call
sites that still need it.
Add AnimatedDecodedImageData which implements DecodedImageData with
an 8-slot buffer pool instead of storing all frames in memory.
Frames are requested on demand from the ImageDecoder service as
the animation progresses.
For a 344-frame animated image at 1920x1080, this reduces
WebContent memory from ~1.3 GB to ~66 MB.
The streaming class owns frame progression and synchronizes
multiple callers (HTMLImageElement and ImageStyleValue) through
notify_frame_advanced() returning the authoritative frame index.
When a frame isn't in the pool, the last displayed frame is shown
as a fallback (brief freeze rather than blank).
Rename the old AnimatedBitmapDecodedImageData (which now only
handles static/single-frame images) to BitmapDecodedImageData.
