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script: No longer do explicit reflows for display (#34599)

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These all happen now in *update the rendering*, typically after the
message that triggered this code is processed, though in two cases
reflow needs to be triggered explicitly. This makes `ReflowReason`
redundant though perhaps `ReflowCondition` can be expanded later to give
more insight into why the page is dirty.

- Handling of the "reflow timer" concept has been explained a bit more via
  data structures and rustdoc comments.
- Theme changes are cleaned up a little to simplify what happens during
  reflow and to avoid unecessary reflows when the theme doesn't change.

Notably, layout queries and scrolling still trigger normal reflows and
don't update the rendering. This needs more investigation as it's
unclear to me currently whether or not they should update the rendering
and simply delay event dispatch or only reflow.

In general, this is a simplfication of the code.

Fixes #31871.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Martin Robinson 2024-12-13 14:25:47 +01:00 • committed by GitHub
parent 682eba9f74
commit 471d3572b7
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9 changed files with 179 additions and 191 deletions
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221
components/script/dom/window.rs
View file

@ -13,7 +13,7 @@ use std::ptr::NonNull;
use std::rc::Rc;
use std::sync::atomic::Ordering;
use std::sync::{Arc, Mutex};
use std::time::Duration;
use std::time::{Duration, Instant};
use app_units::Au;
use backtrace::Backtrace;
@ -72,6 +72,7 @@ use style::media_queries;
use style::parser::ParserContext as CssParserContext;
use style::properties::style_structs::Font;
use style::properties::PropertyId;
use style::queries::values::PrefersColorScheme;
use style::selector_parser::PseudoElement;
use style::str::HTML_SPACE_CHARACTERS;
use style::stylesheets::{CssRuleType, Origin, UrlExtraData};
@ -167,20 +168,36 @@ enum WindowState {
Zombie, // Pipeline is closed, but the window hasn't been GCed yet.
}
/// Extra information concerning the reason for reflowing.
#[derive(Debug, MallocSizeOf)]
pub enum ReflowReason {
CachedPageNeededReflow,
ElementStateChanged,
FirstLoad,
Query,
RefreshTick,
RequestAnimationFrame,
ScrollFromScript,
UpdateTheRendering,
Viewport,
WorkletLoaded,
ThemeChange,
/// How long we should wait before performing the initial reflow after `<body>` is parsed,
/// assuming that `<body>` take this long to parse.
const INITIAL_REFLOW_DELAY: Duration = Duration::from_millis(200);
/// During loading and parsing, layouts are suppressed to avoid flashing incomplete page
/// contents.
///
/// Exceptions:
/// - Parsing the body takes so long, that layouts are no longer suppressed in order
/// to show the user that the page is loading.
/// - Script triggers a layout query or scroll event in which case, we want to layout
/// but not display the contents.
///
/// For more information see: <https://github.com/servo/servo/pull/6028>.
#[derive(Clone, Copy, MallocSizeOf)]
enum LayoutBlocker {
/// The first load event hasn't been fired and we have not started to parse the `<body>` yet.
WaitingForParse,
/// The body is being parsed the `<body>` starting at the `Instant` specified.
Parsing(Instant),
/// The body finished parsing and the `load` event has been fired or parsing took so
/// long, that we are going to do layout anyway. Note that subsequent changes to the body
/// can trigger parsing again, but the `Window` stays in this state.
FiredLoadEventOrParsingTimerExpired,
}
impl LayoutBlocker {
fn layout_blocked(&self) -> bool {
!matches!(self, Self::FiredLoadEventOrParsingTimerExpired)
}
}
#[dom_struct]
@ -226,7 +243,7 @@ pub struct Window {
/// Platform theme.
#[no_trace]
theme: Cell<Theme>,
theme: Cell<PrefersColorScheme>,
/// Parent id associated with this page, if any.
#[no_trace]
@ -255,10 +272,11 @@ pub struct Window {
#[no_trace]
page_clip_rect: Cell<UntypedRect<Au>>,
/// Flag to suppress reflows. The first reflow will come either with
/// RefreshTick or with FirstLoad. Until those first reflows, we want to
/// suppress others like MissingExplicitReflow.
suppress_reflow: Cell<bool>,
/// See the documentation for [`LayoutBlocker`]. Essentially, this flag prevents
/// layouts from happening before the first load event, apart from a few exceptional
/// cases.
#[no_trace]
layout_blocker: Cell<LayoutBlocker>,
/// A channel for communicating results of async scripts back to the webdriver server
#[ignore_malloc_size_of = "channels are hard"]
@ -1769,7 +1787,6 @@ impl Window {
scroll_id,
scroll_offset: Vector2D::new(-x, -y),
}),
ReflowReason::ScrollFromScript,
can_gc,
);
}
@ -1809,41 +1826,30 @@ impl Window {
ScriptThread::handle_tick_all_animations_for_testing(pipeline_id);
}
pub(crate) fn reflows_suppressed(&self) -> bool {
self.suppress_reflow.get()
}
/// Reflows the page unconditionally if possible and not suppressed. This method will wait for
/// the layout to complete. If there is no window size yet, the page is presumed invisible and
/// no reflow is performed. If reflow is suppressed, no reflow will be performed for ForDisplay
/// goals.
///
/// Returns true if layout actually happened, false otherwise.
///
/// NOTE: This method should almost never be called directly! Layout and rendering updates should
/// happen as part of the HTML event loop via *update the rendering*.
#[allow(unsafe_code)]
pub(crate) fn force_reflow(
fn force_reflow(
&self,
reflow_goal: ReflowGoal,
reason: ReflowReason,
condition: Option<ReflowTriggerCondition>,
) -> bool {
self.Document().ensure_safe_to_run_script_or_layout();
// Check if we need to unsuppress reflow. Note that this needs to be
// *before* any early bailouts, or reflow might never be unsuppresed!
match reason {
ReflowReason::FirstLoad | ReflowReason::RefreshTick => self.suppress_reflow.set(false),
_ => (),
}
let for_display = reflow_goal.needs_display();
// If layouts are blocked, we block all layouts that are for display only. Other
// layouts (for queries and scrolling) are not blocked, as they do not display
// anything and script excpects the layout to be up-to-date after they run.
let layout_blocked = self.layout_blocker.get().layout_blocked();
let pipeline_id = self.upcast::<GlobalScope>().pipeline_id();
// If this was just a normal reflow (not triggered by script which forces reflow),
// and the document is still suppressing reflows, exit early.
if reflow_goal == ReflowGoal::Full && self.suppress_reflow.get() {
debug!(
"Suppressing reflow pipeline {} for reason {:?} before FirstLoad or RefreshTick",
pipeline_id, reason
);
if reflow_goal == ReflowGoal::UpdateTheRendering && layout_blocked {
debug!("Suppressing pre-load-event reflow pipeline {pipeline_id}");
return false;
}
@ -1860,8 +1866,7 @@ impl Window {
debug!("Not invalidating cached layout values for paint-only reflow.");
}
debug!("script: performing reflow for reason {:?}", reason);
debug!("script: performing reflow for goal {reflow_goal:?}");
let marker = if self.need_emit_timeline_marker(TimelineMarkerType::Reflow) {
Some(TimelineMarker::start("Reflow".to_owned()))
} else {
@ -1873,7 +1878,7 @@ impl Window {
// On debug mode, print the reflow event information.
if self.relayout_event {
debug_reflow_events(pipeline_id, &reflow_goal, &reason);
debug_reflow_events(pipeline_id, &reflow_goal);
}
let document = self.Document();
@ -1882,6 +1887,7 @@ impl Window {
// If this reflow is for display, ensure webgl canvases are composited with
// up-to-date contents.
let for_display = reflow_goal.needs_display();
if for_display {
#[cfg(feature = "webgpu")]
document.flush_dirty_webgpu_canvases();
@ -1896,11 +1902,6 @@ impl Window {
.or_else(|| document.GetDocumentElement())
.map(|root| root.upcast::<Node>().to_trusted_node_address());
let theme = match self.theme.get() {
Theme::Light => style::queries::values::PrefersColorScheme::Light,
Theme::Dark => style::queries::values::PrefersColorScheme::Dark,
};
// Send new document and relevant styles to layout.
let reflow = ScriptReflow {
reflow_info: Reflow {
@ -1917,7 +1918,7 @@ impl Window {
pending_restyles,
animation_timeline_value: document.current_animation_timeline_value(),
animations: document.animations().sets.clone(),
theme,
theme: self.theme.get(),
};
self.layout.borrow_mut().reflow(reflow);
@ -1977,26 +1978,25 @@ impl Window {
true
}
/// Reflows the page if it's possible to do so and the page is dirty.
/// Reflows the page if it's possible to do so and the page is dirty. Returns true if layout
/// actually happened, false otherwise.
///
/// Returns true if layout actually happened, false otherwise.
/// This return value is useful for script queries, that wait for a lock
/// that layout might hold if the first layout hasn't happened yet (which
/// may happen in the only case a query reflow may bail out, that is, if the
/// viewport size is not present). See #11223 for an example of that.
pub fn reflow(&self, reflow_goal: ReflowGoal, reason: ReflowReason, can_gc: CanGc) -> bool {
/// NOTE: This method should almost never be called directly! Layout and rendering updates
/// should happen as part of the HTML event loop via *update the rendering*. Currerntly, the
/// only exceptions are script queries and scroll requests.
pub(crate) fn reflow(&self, reflow_goal: ReflowGoal, can_gc: CanGc) -> bool {
// Fetch the pending web fonts before layout, in case a font loads during
// the layout.
let pending_web_fonts = self.layout.borrow().waiting_for_web_fonts_to_load();
self.Document().ensure_safe_to_run_script_or_layout();
let for_display = reflow_goal == ReflowGoal::Full;
let mut issued_reflow = false;
let condition = self.Document().needs_reflow();
if !for_display || condition.is_some() {
let updating_the_rendering = reflow_goal == ReflowGoal::UpdateTheRendering;
if !updating_the_rendering || condition.is_some() {
debug!("Reflowing document ({:?})", self.pipeline_id());
issued_reflow = self.force_reflow(reflow_goal, reason, condition);
issued_reflow = self.force_reflow(reflow_goal, condition);
// We shouldn't need a reflow immediately after a
// reflow, except if we're waiting for a deferred paint.
@ -2004,16 +2004,16 @@ impl Window {
assert!(
{
condition.is_none() ||
(!for_display &&
(!updating_the_rendering &&
condition == Some(ReflowTriggerCondition::PaintPostponed)) ||
self.suppress_reflow.get()
self.layout_blocker.get().layout_blocked()
},
"condition was {:?}",
condition
);
} else {
debug!(
"Document ({:?}) doesn't need reflow - skipping it (reason {reason:?})",
"Document ({:?}) doesn't need reflow - skipping it (goal {reflow_goal:?})",
self.pipeline_id()
);
}
@ -2044,7 +2044,7 @@ impl Window {
// When all these conditions are met, notify the constellation
// that this pipeline is ready to write the image (from the script thread
// perspective at least).
if self.prepare_for_screenshot && for_display {
if self.prepare_for_screenshot && updating_the_rendering {
// Checks if the html element has reftest-wait attribute present.
// See http://testthewebforward.org/docs/reftests.html
// and https://web-platform-tests.org/writing-tests/crashtest.html
@ -2076,6 +2076,66 @@ impl Window {
issued_reflow
}
/// If parsing has taken a long time and reflows are still waiting for the `load` event,
/// start allowing them. See <https://github.com/servo/servo/pull/6028>.
pub(crate) fn reflow_if_reflow_timer_expired(&self, can_gc: CanGc) {
// Only trigger a long parsing time reflow if we are in the first parse of `<body>`
// and it started more than `INITIAL_REFLOW_DELAY` ago.
if !matches!(
self.layout_blocker.get(),
LayoutBlocker::Parsing(instant) if instant + INITIAL_REFLOW_DELAY < Instant::now()
) {
return;
}
self.allow_layout_if_necessary(can_gc);
}
/// Block layout for this `Window` until parsing is done. If parsing takes a long time,
/// we want to layout anyway, so schedule a moment in the future for when layouts are
/// allowed even though parsing isn't finished and we havne't sent a load event.
pub(crate) fn prevent_layout_until_load_event(&self) {
// If we have already started parsing or have already fired a load event, then
// don't delay the first layout any longer.
if !matches!(self.layout_blocker.get(), LayoutBlocker::WaitingForParse) {
return;
}
self.layout_blocker
.set(LayoutBlocker::Parsing(Instant::now()));
}
/// Inform the [`Window`] that layout is allowed either because `load` has happened
/// or because parsing the `<body>` took so long that we cannot wait any longer.
pub(crate) fn allow_layout_if_necessary(&self, can_gc: CanGc) {
if matches!(
self.layout_blocker.get(),
LayoutBlocker::FiredLoadEventOrParsingTimerExpired
) {
return;
}
self.layout_blocker
.set(LayoutBlocker::FiredLoadEventOrParsingTimerExpired);
self.Document().set_needs_paint(true);
// We do this immediately instead of scheduling a future task, because this can
// happen if parsing is taking a very long time, which means that the
// `ScriptThread` is busy doing the parsing and not doing layouts.
//
// TOOD(mrobinson): It's expected that this is necessary when in the process of
// parsing, as we need to interrupt it to update contents, but why is this
// necessary when parsing finishes? Not doing the synchronous update in that case
// causes iframe tests to become flaky. It seems there's an issue with the timing of
// iframe size updates.
//
// See <https://github.com/servo/servo/issues/14719>
self.reflow(ReflowGoal::UpdateTheRendering, can_gc);
}
pub(crate) fn layout_blocked(&self) -> bool {
self.layout_blocker.get().layout_blocked()
}
/// If writing a screenshot, synchronously update the layout epoch that it set
/// in the constellation.
pub(crate) fn update_constellation_epoch(&self) {
@ -2095,11 +2155,7 @@ impl Window {
}
pub fn layout_reflow(&self, query_msg: QueryMsg, can_gc: CanGc) -> bool {
self.reflow(
ReflowGoal::LayoutQuery(query_msg),
ReflowReason::Query,
can_gc,
)
self.reflow(ReflowGoal::LayoutQuery(query_msg), can_gc)
}
pub fn resolved_font_style_query(
@ -2368,8 +2424,18 @@ impl Window {
self.window_size.get()
}
pub fn set_theme(&self, theme: Theme) {
self.theme.set(theme);
/// Handle a theme change request, triggering a reflow is any actual change occured.
pub(crate) fn handle_theme_change(&self, new_theme: Theme) {
let new_theme = match new_theme {
Theme::Light => PrefersColorScheme::Light,
Theme::Dark => PrefersColorScheme::Dark,
};
if self.theme.get() == new_theme {
return;
}
self.theme.set(new_theme);
self.Document().set_needs_paint(true);
}
pub fn get_url(&self) -> ServoUrl {
@ -2717,7 +2783,7 @@ impl Window {
unhandled_resize_event: Default::default(),
window_size: Cell::new(window_size),
current_viewport: Cell::new(initial_viewport.to_untyped()),
suppress_reflow: Cell::new(true),
layout_blocker: Cell::new(LayoutBlocker::WaitingForParse),
current_state: Cell::new(WindowState::Alive),
devtools_marker_sender: Default::default(),
devtools_markers: Default::default(),
@ -2747,7 +2813,7 @@ impl Window {
throttled: Cell::new(false),
layout_marker: DomRefCell::new(Rc::new(Cell::new(true))),
current_event: DomRefCell::new(None),
theme: Cell::new(Theme::Light),
theme: Cell::new(PrefersColorScheme::Light),
});
unsafe { WindowBinding::Wrap(JSContext::from_ptr(runtime.cx()), win) }
@ -2825,10 +2891,9 @@ fn should_move_clip_rect(clip_rect: UntypedRect<Au>, new_viewport: UntypedRect<f
(clip_rect.max_y() - new_viewport.max_y()).abs() <= viewport_scroll_margin.height
}
fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal, reason: &ReflowReason) {
fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal) {
let goal_string = match *reflow_goal {
ReflowGoal::Full => "\tFull",
ReflowGoal::TickAnimations => "\tTickAnimations",
ReflowGoal::UpdateTheRendering => "\tFull",
ReflowGoal::UpdateScrollNode(_) => "\tUpdateScrollNode",
ReflowGoal::LayoutQuery(ref query_msg) => match *query_msg {
QueryMsg::ContentBox => "\tContentBoxQuery",
@ -2846,7 +2911,7 @@ fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal, reason: &Reflow
},
};
println!("**** pipeline={}\t{}\t{:?}", id, goal_string, reason);
println!("**** pipeline={id}\t{goal_string}");
}
impl Window {