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LibWeb: Implement auto alignment of animation start times

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Nonfunctional change for now since we don't yet have any progress-based
timelines
This commit is contained in:
Callum Law
2025-12-14 19:43:00 +13:00
committed by Jelle Raaijmakers
parent 6df2ebeee1
commit 626caa3af3
Notes: github-actions[bot] 2026-02-06 10:30:23 +00:00 
Author: https://github.com/Calme1709
Commit: https://github.com/LadybirdBrowser/ladybird/commit/626caa3af39
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/7196
Reviewed-by: https://github.com/gmta ✅
2 changed files with 63 additions and 5 deletions
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64
Libraries/LibWeb/Animations/Animation.cpp
View File

@@ -172,7 +172,8 @@ void Animation::set_timeline(GC::Ptr<AnimationTimeline> new_timeline)
// 1. Apply any pending playback rate on animation
apply_any_pending_playback_rate();
// FIXME: 2. set auto align start time to true.
// 2. set auto align start time to true.
m_auto_align_start_time = true;
// 3. Set start time to unresolved.
m_start_time = {};
@@ -280,7 +281,8 @@ WebIDL::ExceptionOr<void> Animation::set_start_time_for_bindings(Optional<CSS::C
// there is no need to assign the `valid start time` variable here.
auto new_start_time = TRY(validate_a_css_numberish_time(raw_new_start_time));
// FIXME: 3. Set auto align start time to false.
// 3. Set auto align start time to false.
m_auto_align_start_time = false;
// 4. Let timeline time be the current time value of the timeline that animation is associated with. If there is no
// timeline associated with animation or the associated timeline is inactive, let the timeline time be
@@ -329,6 +331,47 @@ WebIDL::ExceptionOr<void> Animation::set_start_time_for_bindings(Optional<CSS::C
return {};
}
// https://drafts.csswg.org/web-animations-2/#auto-aligning-start-time
void Animation::calculate_auto_aligned_start_time()
{
VERIFY(m_timeline && m_timeline->is_progress_based());
// 1. If the auto-align start time flag is false, abort this procedure.
if (!m_auto_align_start_time)
return;
// 2. If the timeline is inactive, abort this procedure.
if (!m_timeline || m_timeline->is_inactive())
return;
// 3. If play state is idle, abort this procedure.
if (is_idle())
return;
// 4. If play state is paused, and hold time is resolved, abort this procedure.
if (play_state() == Bindings::AnimationPlayState::Paused && m_hold_time.has_value())
return;
// 5. FIXME: Let start offset be the resolved timeline time corresponding to the start of the animation attachment
// range. In the case of view timelines, it requires a calculation based on the proportion of the cover
// range.
auto start_offset = TimeValue { TimeValue::Type::Percentage, 0 };
// 6. FIXME: Let end offset be the resolved timeline time corresponding to the end of the animation attachment
// range. In the case of view timelines, it requires a calculation based on the proportion of the cover
// range.
auto end_offset = TimeValue { TimeValue::Type::Percentage, 100 };
// 7. Set start time to start offset if effective playback rate ≥ 0, and end offset otherwise.
if (effective_playback_rate() >= 0.0)
m_start_time = start_offset;
else
m_start_time = end_offset;
// 8. Clear hold time.
m_hold_time = {};
}
// https://www.w3.org/TR/web-animations-1/#animation-current-time
Optional<TimeValue> Animation::current_time() const
{
@@ -778,7 +821,8 @@ WebIDL::ExceptionOr<void> Animation::play_an_animation(AutoRewind auto_rewind)
// 7. If has finite timeline and previous current time is unresolved:
if (has_finite_timeline && !previous_current_time.has_value()) {
// FIXME: Set the flag auto align start time to true.
// Set the flag auto align start time to true.
m_auto_align_start_time = true;
}
// 8. If animation’s hold time is resolved, let its start time be unresolved.
@@ -799,7 +843,10 @@ WebIDL::ExceptionOr<void> Animation::play_an_animation(AutoRewind auto_rewind)
// - animation’s hold time is unresolved, and
// - aborted pause is false, and
// - animation does not have a pending playback rate,
if (!m_hold_time.has_value() && !aborted_pause && !m_pending_playback_rate.has_value()) {
// AD-HOC: We also don't abort if we have a pending auto-alignment of the start time, see
// https://github.com/w3c/csswg-drafts/issues/13236
auto pending_auto_aligned_start_time = m_auto_align_start_time && !m_start_time.has_value();
if (!m_hold_time.has_value() && !aborted_pause && !m_pending_playback_rate.has_value() && !pending_auto_aligned_start_time) {
// abort this procedure.
return {};
}
@@ -1073,6 +1120,12 @@ GC::Ptr<DOM::Document> Animation::document_for_timing() const
void Animation::update()
{
// https://drafts.csswg.org/scroll-animations-1/#event-loop
// When updating timeline current time, the start time of any attached animation is conditionally updated. For each
// attached animation, run the procedure for calculating an auto-aligned start time.
if (m_timeline && m_timeline->is_progress_based())
calculate_auto_aligned_start_time();
// Update finished state if not already finished; prevents recurring invalidation when the timeline updates.
if (!m_is_finished)
update_finished_state(DidSeek::No, SynchronouslyNotify::Yes);
@@ -1145,7 +1198,8 @@ WebIDL::ExceptionOr<void> Animation::silently_set_current_time(Optional<TimeValu
// 3. If valid seek time is false, abort this procedure.
// AD-HOC: We have already validated in the caller.
// FIXME: 4. Set auto align start time to false.
// 4. Set auto align start time to false.
m_auto_align_start_time = false;
// 5. Update either animation’s hold time or start time as follows: