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throttle scroll event

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This commit is contained in:
Pierre Tachoire
2025-12-23 16:06:33 +01:00
parent 2b10b1c17a
commit 2bd38608e9
2 changed files with 108 additions and 12 deletions
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42
src/browser/tests/window/scroll.html Normal file
View File

@@ -0,0 +1,42 @@
<!DOCTYPE html>
<script src="../testing.js"></script>
<!-- Chrome don't scroll if the body isn't big enough. -->
<body style=height:4000px;width:4000px></body>
<script id=scroll_evt>
testing.async(async (restore) => {
let scrollevt = 0;
let scrollendevt = 0;
await new Promise((resolve) => {
document.addEventListener("scroll", (event) => {
scrollevt++;
});
document.addEventListener("scrollend", (event) => {
scrollendevt++;
});
window.scrollTo(10, 20);
testing.expectEqual(0, scrollevt);
testing.expectEqual(0, scrollendevt);
// scroll immediately: the scroll event must be throttled.
window.scrollTo(20, 40);
testing.expectEqual(0, scrollevt);
testing.expectEqual(0, scrollendevt);
// wait 10ms and scroll again: we should have a 2nd scroll, but no scrollend.
window.setTimeout(() => {
window.scrollTo(30, 40);
}, 10);
// wait until scrollend happens.
window.setTimeout(() => {
resolve();
}, 100);
});
restore();
testing.expectEqual(2, scrollevt);
testing.expectEqual(1, scrollendevt);
});
</script>

78
src/browser/webapi/Window.zig
View File

@@ -63,7 +63,19 @@ _location: *Location,
_timer_id: u30 = 0,
_timers: std.AutoHashMapUnmanaged(u32, *ScheduleCallback) = .{},
_custom_elements: CustomElementRegistry = .{},
_scroll_pos: struct { x: u32, y: u32 } = .{ .x = 0, .y = 0 },
_scroll_pos: struct {
x: u32,
y: u32,
state: enum {
scroll,
end,
done,
},
} = .{
.x = 0,
.y = 0,
.state = .done,
},
pub fn asEventTarget(self: *Window) *EventTarget {
return self._proto;
@@ -387,18 +399,60 @@ pub fn scrollTo(self: *Window, opts: ScrollToOpts, y: ?i32, page: *Page) !void {
},
}
{
// TODO According to the doc, scroll event should be throttled.
// see https://developer.mozilla.org/en-US/docs/Web/API/Document/scroll_event#scroll_event_throttling
const event = try Event.init("scroll", .{ .bubbles = true }, page);
try page._event_manager.dispatch(self._document.asEventTarget(), event);
}
self._scroll_pos.state = .scroll;
{
// TODO scrollend must be dispatched once the scroll really ends.
const event = try Event.init("scrollend", .{ .bubbles = true }, page);
try page._event_manager.dispatch(self._document.asEventTarget(), event);
}
// We dispatch scroll event asynchronously after 10ms. So we can throttle
// them.
try page.scheduler.add(
page,
struct {
fn dispatch(_page: *anyopaque) anyerror!?u32 {
const p: *Page = @ptrCast(@alignCast(_page));
const pos = &p.window._scroll_pos;
// If the state isn't scroll, we can ignore safely to throttle
// the events.
if (pos.state != .scroll) {
return null;
}
const event = try Event.init("scroll", .{ .bubbles = true }, p);
try p._event_manager.dispatch(p.document.asEventTarget(), event);
pos.state = .end;
return null;
}
}.dispatch,
10,
.{ .low_priority = true },
);
// We dispatch scrollend event asynchronously after 20ms.
try page.scheduler.add(
page,
struct {
fn dispatch(_page: *anyopaque) anyerror!?u32 {
const p: *Page = @ptrCast(@alignCast(_page));
const pos = &p.window._scroll_pos;
// Dispatch only if the state is .end.
// If a scroll is pending, retry in 10ms.
// If the state is .end, the event has been dispatched, so
// ignore safely.
switch (pos.state) {
.scroll => return 10,
.end => {},
.done => return null,
}
const event = try Event.init("scrollend", .{ .bubbles = true }, p);
try p._event_manager.dispatch(p.document.asEventTarget(), event);
pos.state = .done;
return null;
}
}.dispatch,
20,
.{ .low_priority = true },
);
}
const ScheduleOpts = struct {