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Merged
yezhizhen merged 3 commits into from
Mar 11, 2026
Merged

webdriver: Support interspersed scroll actions via event queue #43126

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a44f2bb
Remove loop and fmt
yezhizhen Mar 10, 2026
6329e43
event loop
yezhizhen Mar 10, 2026
7c724b1
Add wdspec interspersed wheel/pointermove event test
yezhizhen Mar 10, 2026
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261 changes: 167 additions & 94 deletions components/webdriver_server/actions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,8 +28,7 @@ use webdriver::error::{ErrorStatus, WebDriverError};
use crate::{Handler, VerifyBrowsingContextIsOpen, WebElement, wait_for_oneshot_response};

/// Interval between wheelScroll and pointerMove increments in ms, based on common vsync
static POINTERMOVE_INTERVAL: u64 = 16;
static WHEELSCROLL_INTERVAL: u64 = 16;
static MOVESCROLL_INTERVAL: u64 = 16;

/// <https://w3c.github.io/webdriver/#dfn-element-click>
/// This is hard-coded as 0 in spec.
Expand Down Expand Up @@ -66,7 +65,28 @@ pub(crate) enum InputSourceState {
Wheel,
}

pub(crate) struct PendingPointerMove {
#[expect(private_interfaces)]

@yezhizhen yezhizhen Mar 10, 2026

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This is to suppress

warning: type `PendingScroll` is more private than the item `PendingActions::Scroll::0`
  --> components\webdriver_server\actions.rs:69:12
   |
69 |     Scroll(PendingScroll),
   |            ^^^^^^^^^^^^^ field `PendingActions::Scroll::0` is reachable at visibility `pub(crate)`

For our case, we just need PendingActions to be seen in lib.rs to declare Vec<PendingActions>.

pub(crate) enum PendingActions {
Scroll(PendingScroll),
PointerMove(PendingPointerMove),
}

/// <https://github.com/w3c/webdriver/issues/1952>
/// For some unknown reason, unlike Pointer Actions,
/// Wheel Actions in spec has precision of integer.
/// We just use double precision, since our [`WheelEvent`] also uses double precision.
struct PendingScroll {
input_id: String,
duration: u64,
x: f64,
y: f64,
current_delta_x: f64,
current_delta_y: f64,
target_delta_x: f64,
target_delta_y: f64,
}

struct PendingPointerMove {
input_id: String,
duration: u64,
start_x: f64,
Expand Down Expand Up @@ -181,7 +201,7 @@ impl Handler {

// Step 1.3. Try to dispatch tick actions
self.dispatch_tick_actions(tick_actions, tick_duration, &tick_start)?;
self.process_pending_pointer_moves(&tick_start);
self.process_pending_actions(&tick_start);
// Step 1.4.1
// There are no pending asynchronous waits arising
// from the last invocation of the dispatch tick actions steps.
Expand Down Expand Up @@ -215,22 +235,52 @@ impl Handler {
/// Step 9.1. Asynchronously wait for an implementation defined amount of time to pass.
/// Step 9.2. Perform a pointer move with arguments input state,
/// duration, start x, start y, target x, target y.
fn process_pending_pointer_moves(&mut self, tick_start: &Instant) {
while !self.pending_pointer_moves.is_empty() {
let moves = std::mem::take(&mut self.pending_pointer_moves);
thread::sleep(Duration::from_millis(POINTERMOVE_INTERVAL));
for PendingPointerMove {
input_id,
duration,
start_x,
start_y,
target_x,
target_y,
} in moves
{
self.perform_pointer_move(
&input_id, duration, start_x, start_y, target_x, target_y, tick_start,
);
/// <https://w3c.github.io/webdriver/#dfn-perform-a-scroll>
/// Step 7. Run the following substeps in parallel:
/// Step 7.1. Asynchronously wait for an implementation defined amount of time to pass.
/// Step 7.2. Perform a scroll with arguments duration, x, y,
/// target delta x, target delta y, current delta x, current delta y.
fn process_pending_actions(&mut self, tick_start: &Instant) {
while !self.pending_actions.is_empty() {
let pending_actions = std::mem::take(&mut self.pending_actions);
thread::sleep(Duration::from_millis(MOVESCROLL_INTERVAL));
for action in pending_actions {
match action {
PendingActions::PointerMove(PendingPointerMove {
input_id,
duration,
start_x,
start_y,
target_x,
target_y,
}) => {
self.perform_pointer_move(
&input_id, duration, start_x, start_y, target_x, target_y, tick_start,
);
},
PendingActions::Scroll(PendingScroll {
input_id,
duration,
x,
y,
current_delta_x,
current_delta_y,
target_delta_x,
target_delta_y,
}) => {
self.perform_scroll(
&input_id,
duration,
x,
y,
target_delta_x,
target_delta_y,
current_delta_x,
current_delta_y,
tick_start,
);
},
}
}
}
}
Expand Down Expand Up @@ -540,7 +590,7 @@ impl Handler {
// Asynchronously wait means do not block browser to process event loop.
// In the context of Servo, it means block the webdriver server thread.
if duration > 0 {
thread::sleep(Duration::from_millis(POINTERMOVE_INTERVAL));
thread::sleep(Duration::from_millis(MOVESCROLL_INTERVAL));
}

let (start_x, start_y) = {
Expand Down Expand Up @@ -669,14 +719,15 @@ impl Handler {
// We use [`PendingPointerMove`] to achieve the same effect as asynchronous wait and
// parallelism required by spec.
// This conveniently unify the wait interval between ticks.
self.pending_pointer_moves.push(PendingPointerMove {
input_id: input_id.to_owned(),
duration,
start_x,
start_y,
target_x,
target_y,
});
self.pending_actions
.push(PendingActions::PointerMove(PendingPointerMove {
input_id: input_id.to_owned(),
duration,
start_x,
start_y,
target_x,
target_y,
}));
}

/// <https://w3c.github.io/webdriver/#dfn-dispatch-a-scroll-action>
Expand Down Expand Up @@ -742,11 +793,12 @@ impl Handler {
// Step 10. If duration is greater than 0 and inside any implementation-defined bounds,
// asynchronously wait for an implementation defined amount of time to pass.
if duration > 0 {
thread::sleep(Duration::from_millis(WHEELSCROLL_INTERVAL));
thread::sleep(Duration::from_millis(MOVESCROLL_INTERVAL));
}

// Step 11. Perform a scroll with arguments global key state, duration, x, y, delta x, delta y, 0, 0.
self.perform_scroll(
input_id,
duration,
x,
y,
Expand All @@ -765,85 +817,106 @@ impl Handler {
#[expect(clippy::too_many_arguments)]
fn perform_scroll(
&mut self,
input_id: &str,
duration: u64,
x: f64,
y: f64,
target_delta_x: f64,
target_delta_y: f64,
mut curr_delta_x: f64,
mut curr_delta_y: f64,
mut current_delta_x: f64,
mut current_delta_y: f64,
tick_start: &Instant,
) {
loop {
// Step 1. Let time delta be the time since the beginning of the current tick,
// measured in milliseconds on a monotonic clock.
let time_delta = tick_start.elapsed().as_millis();

// Step 2. Let duration ratio be the ratio of time delta and duration,
// if duration is greater than 0, or 1 otherwise.
let duration_ratio = if duration > 0 {
time_delta as f64 / duration as f64
} else {
1.0
};
// Step 1. Let time delta be the time since the beginning of the current tick,
// measured in milliseconds on a monotonic clock.
let time_delta = tick_start.elapsed().as_millis();

// Step 3. If duration ratio is 1, or close enough to 1 that
// the implementation will not further subdivide the move action,
// let last be true. Otherwise let last be false.
let last = 1.0 - duration_ratio < 0.001;

// Step 4. If last is true,
// let delta x equal target delta x - current delta x and delta y equal target delta y - current delta y.
// Otherwise
// let delta x equal an approximation to duration ratio × target delta x - current delta x,
// and delta y equal an approximation to duration ratio × target delta y - current delta y.
let (delta_x, delta_y) = if last {
(target_delta_x - curr_delta_x, target_delta_y - curr_delta_y)
} else {
(
duration_ratio * target_delta_x - curr_delta_x,
duration_ratio * target_delta_y - curr_delta_y,
)
};
// Step 2. Let duration ratio be the ratio of time delta and duration,
// if duration is greater than 0, or 1 otherwise.
let duration_ratio = if duration > 0 {
time_delta as f64 / duration as f64
} else {
1.0
};

// Step 5. If delta x != 0 or delta y != 0, run the following steps:
// Actually "last" should not be checked here based on spec.
// However, we need to send the webdriver id at the final perform.
if delta_x != 0.0 || delta_y != 0.0 || last {
// Step 5.1. Perform implementation-specific action dispatch steps
let delta = WheelDelta {
x: -delta_x,
y: -delta_y,
z: 0.0,
mode: WheelMode::DeltaPixel,
};
let point = WebViewPoint::Page(Point2D::new(x as f32, y as f32));
let input_event = InputEvent::Wheel(WheelEvent::new(delta, point));
if last {
self.send_blocking_input_event_to_embedder(input_event);
} else {
self.send_input_event_to_embedder(input_event);
}
// Step 3. If duration ratio is 1, or close enough to 1 that
// the implementation will not further subdivide the move action,
// let last be true. Otherwise let last be false.
let last = 1.0 - duration_ratio < 0.001;

// Step 5.2. Let current delta x property equal delta x + current delta x
// and current delta y property equal delta y + current delta y.
curr_delta_x += delta_x;
curr_delta_y += delta_y;
}
// Step 4. If last is true,
// let delta x equal target delta x - current delta x and delta y equal target delta y - current delta y.
// Otherwise
// let delta x equal an approximation to duration ratio × target delta x - current delta x,
// and delta y equal an approximation to duration ratio × target delta y - current delta y.
let (delta_x, delta_y) = if last {
(
target_delta_x - current_delta_x,
target_delta_y - current_delta_y,
)
} else {
(
duration_ratio * target_delta_x - current_delta_x,
duration_ratio * target_delta_y - current_delta_y,
)
};

// Step 6. If last is true, return.
// Step 5. If delta x != 0 or delta y != 0, run the following steps:
// Actually "last" should not be checked here based on spec.
// However, we need to send the webdriver id at the final perform.
if delta_x != 0.0 || delta_y != 0.0 || last {
// Step 5.1. Perform implementation-specific action dispatch steps
let delta = WheelDelta {
x: -delta_x,
y: -delta_y,
z: 0.0,
mode: WheelMode::DeltaPixel,
};
let point = WebViewPoint::Page(Point2D::new(x as f32, y as f32));
let input_event = InputEvent::Wheel(WheelEvent::new(delta, point));
if last {
return;
self.send_blocking_input_event_to_embedder(input_event);
} else {
self.send_input_event_to_embedder(input_event);
}

// Step 7
// TODO: The two steps should be done in parallel
// 7.1. Asynchronously wait for an implementation defined amount of time to pass.
thread::sleep(Duration::from_millis(WHEELSCROLL_INTERVAL));
// 7.2. Perform a scroll with arguments duration, x, y, target delta x,
// target delta y, current delta x, current delta y.
// Notice that this simply repeat what we have done until last is true.
// Step 5.2. Let current delta x property equal delta x + current delta x
// and current delta y property equal delta y + current delta y.
current_delta_x += delta_x;
current_delta_y += delta_y;
}

// Step 6. If last is true, return.
if last {
return;
}

// Step 7. Run the following substeps in parallel:
// Step 7.1. Asynchronously wait for an implementation defined amount of time to pass.
// Step 7.2. Perform a scroll with arguments duration, x, y,
// target delta x, target delta y, current delta x, current delta y.
// This is done in `fn process_pending_actions`.

// NOTE: The initial scroll is performed synchronously.
// This ensures determinism in the sequence of the first event
// triggered by each action in the tick.
// Subsequent scrolls (if any) are performed asynchronously.
// This allows events from two scroll actions in the tick to be interspersed.

// We use [`PendingScroll`] to achieve the same effect as asynchronous wait and
// parallelism required by spec.
// This conveniently unify the wait interval between ticks.
self.pending_actions
.push(PendingActions::Scroll(PendingScroll {
input_id: input_id.to_owned(),
duration,
x,
y,
current_delta_x,
current_delta_y,
target_delta_x,
target_delta_y,
}));
}

/// Verify that the given coordinates are within the boundary of the viewport.
Expand Down
11 changes: 5 additions & 6 deletions components/webdriver_server/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,9 +73,7 @@ use webdriver::response::{
};
use webdriver::server::{self, Session, SessionTeardownKind, WebDriverHandler};

use crate::actions::{
ELEMENT_CLICK_BUTTON, InputSourceState, PendingPointerMove, PointerInputState,
};
use crate::actions::{ELEMENT_CLICK_BUTTON, InputSourceState, PendingActions, PointerInputState};
use crate::session::{PageLoadStrategy, WebDriverSession};
use crate::timeout::{DEFAULT_IMPLICIT_WAIT, DEFAULT_PAGE_LOAD_TIMEOUT, SCREENSHOT_TIMEOUT};

Expand Down Expand Up @@ -183,8 +181,9 @@ struct Handler {
/// TODO: Once we upgrade crossbeam-channel this can be replaced with a `WaitGroup`.
pending_input_event_receivers: Vec<Receiver<()>>,

/// Moves that are currently in-progress and need to be ticked.
pending_pointer_moves: Vec<PendingPointerMove>,
/// Ongoing [`PointerMoveAction`] or [`WheelScrollAction`] that are being incrementally
/// processed across multiple execution cycles within the current tick.
pending_actions: Vec<PendingActions>,

@yezhizhen yezhizhen Mar 10, 2026

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this one.


/// The base set of preferences to treat as default when resetting.
default_preferences: Preferences,
Expand Down Expand Up @@ -468,7 +467,7 @@ impl Handler {
event_loop_waker,
default_preferences,
pending_input_event_receivers: Default::default(),
pending_pointer_moves: Default::default(),
pending_actions: Default::default(),
}
}

Expand Down
2 changes: 1 addition & 1 deletion tests/wpt/meta/MANIFEST.json
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Original file line number Diff line number Diff line change
Expand Up @@ -990350,7 +990350,7 @@
]
],
"perform.py": [
"30333942189c6f01ece57e49e45be9c5a5412e70",
"55aca8fd84ae0ef80f65245bbeade0cd462cf4c6",
[
null,
{}
Expand Down
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