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LibWeb: Rasterize each Navigable independently on its own thread

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Previously, iframes were rasterized synchronously as nested display
lists inside their parent's display list: the parent's paint walk called
record_display_list() on each hosted iframe document and emitted a
PaintNestedDisplayList command that the player would recurse into. Only
the top-level traversable's RenderingThread was ever active, even though
every Navigable already owned one.

The motivation for splitting this apart:
- Work in the outer document no longer has to be re-recorded when only
  an iframe changes. The parent's cached display list now references the
  iframe's rasterized output live via an ExternalContentSource, so an
  iframe invalidation just needs the parent's display list replayed, not
  re-recorded.
- Each iframe now has a self-contained rasterization pipeline, which is
  prep work for moving iframes into separate sandboxed processes.
This commit is contained in:
Aliaksandr Kalenik
2026-04-05 17:00:40 +02:00
committed by Alexander Kalenik
parent 115531eef1
commit ad2ee4fe7a
Notes: github-actions[bot] 2026-04-07 13:10:43 +00:00 
Author: https://github.com/kalenikaliaksandr
Commit: https://github.com/LadybirdBrowser/ladybird/commit/ad2ee4fe7ac
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/8793
8 changed files with 132 additions and 82 deletions
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81
Libraries/LibWeb/HTML/RenderingThread.cpp
View File

@@ -5,11 +5,16 @@
*/
#include <LibCore/EventLoop.h>
#include <LibGfx/ImmutableBitmap.h>
#include <LibGfx/PaintingSurface.h>
#include <LibThreading/Thread.h>
#include <LibWeb/HTML/RenderingThread.h>
#include <LibWeb/HTML/TraversableNavigable.h>
#include <LibWeb/Painting/DisplayListPlayerSkia.h>
#include <LibWeb/Painting/ExternalContentSource.h>
#include <core/SkCanvas.h>
#include <core/SkColor.h>
#include <LibCore/Platform/ScopedAutoreleasePool.h>
@@ -66,12 +71,19 @@ public:
bool has_skia_player() const { return m_skia_player != nullptr; }
void set_presentation_mode(RenderingThread::PresentationMode mode)
{
Threading::MutexLocker const locker { m_mutex };
m_presentation_mode = move(mode);
}
void exit()
{
Threading::MutexLocker const locker { m_mutex };
m_exit = true;
m_command_ready.signal();
m_ready_to_paint.signal();
m_frame_completed.broadcast();
}
void enqueue_command(CompositorCommand&& command)
@@ -81,12 +93,28 @@ public:
m_command_ready.signal();
}
void set_needs_present(Gfx::IntRect viewport_rect)
u64 set_needs_present(Gfx::IntRect viewport_rect)
{
Threading::MutexLocker const locker { m_mutex };
m_needs_present = true;
m_pending_viewport_rect = viewport_rect;
m_submitted_frame_id++;
m_command_ready.signal();
return m_submitted_frame_id;
}
void mark_frame_complete(u64 frame_id)
{
Threading::MutexLocker const locker { m_mutex };
m_completed_frame_id = frame_id;
m_frame_completed.broadcast();
}
void wait_for_frame(u64 frame_id)
{
Threading::MutexLocker const locker { m_mutex };
while (m_completed_frame_id < frame_id && !m_exit)
m_frame_completed.wait();
}
void compositor_loop()
@@ -147,11 +175,13 @@ public:
bool should_present = false;
Gfx::IntRect viewport_rect;
u64 presenting_frame_id = 0;
{
Threading::MutexLocker const locker { m_mutex };
if (m_needs_present) {
should_present = true;
viewport_rect = m_pending_viewport_rect;
presenting_frame_id = m_submitted_frame_id;
m_needs_present = false;
}
}
@@ -167,17 +197,37 @@ public:
break;
}
auto presentation_mode = [this] {
Threading::MutexLocker const locker { m_mutex };
return m_presentation_mode;
}();
if (m_cached_display_list && m_backing_stores.is_valid()) {
auto should_clear_back_store = presentation_mode.visit(
[](RenderingThread::PresentToUI) { return false; },
[](RenderingThread::PublishToExternalContent const&) { return true; });
if (should_clear_back_store) {
// Embedded navigables leave their PaintConfig canvas unfilled, so double-buffered back stores
// must be cleared before repainting.
m_backing_stores.back_store->canvas().clear(SK_ColorTRANSPARENT);
}
m_skia_player->execute(*m_cached_display_list, Painting::ScrollStateSnapshotByDisplayList(m_cached_scroll_state_snapshot), *m_backing_stores.back_store);
i32 rendered_bitmap_id = m_backing_stores.back_bitmap_id;
m_backing_stores.swap();
m_queued_rasterization_tasks++;
invoke_on_main_thread([this, viewport_rect, rendered_bitmap_id]() {
m_presentation_callback(viewport_rect, rendered_bitmap_id);
});
presentation_mode.visit(
[this, viewport_rect, rendered_bitmap_id](RenderingThread::PresentToUI) {
m_queued_rasterization_tasks++;
invoke_on_main_thread([this, viewport_rect, rendered_bitmap_id]() {
m_presentation_callback(viewport_rect, rendered_bitmap_id);
});
},
[this](RenderingThread::PublishToExternalContent const& mode) {
auto snapshot = Gfx::ImmutableBitmap::create_snapshot_from_painting_surface(*m_backing_stores.front_store);
mode.source->update(move(snapshot));
});
}
mark_frame_complete(presenting_frame_id);
}
}
}
@@ -209,6 +259,7 @@ private:
RefPtr<Painting::DisplayList> m_cached_display_list;
Painting::ScrollStateSnapshotByDisplayList m_cached_scroll_state_snapshot;
BackingStoreState m_backing_stores;
RenderingThread::PresentationMode m_presentation_mode { RenderingThread::PresentToUI {} };
Atomic<i32> m_queued_rasterization_tasks { 0 };
mutable Threading::ConditionVariable m_ready_to_paint { m_mutex };
@@ -216,6 +267,10 @@ private:
bool m_needs_present { false };
Gfx::IntRect m_pending_viewport_rect;
u64 m_submitted_frame_id { 0 };
u64 m_completed_frame_id { 0 };
mutable Threading::ConditionVariable m_frame_completed { m_mutex };
public:
void decrement_queued_tasks()
{
@@ -252,6 +307,11 @@ void RenderingThread::set_skia_player(OwnPtr<Painting::DisplayListPlayerSkia>&&
m_thread_data->set_skia_player(move(player));
}
void RenderingThread::set_presentation_mode(PresentationMode mode)
{
m_thread_data->set_presentation_mode(move(mode));
}
void RenderingThread::update_display_list(NonnullRefPtr<Painting::DisplayList> display_list, Painting::ScrollStateSnapshotByDisplayList&& scroll_state_snapshot)
{
m_thread_data->enqueue_command(UpdateDisplayListCommand { move(display_list), move(scroll_state_snapshot) });
@@ -262,9 +322,14 @@ void RenderingThread::update_backing_stores(RefPtr<Gfx::PaintingSurface> front,
m_thread_data->enqueue_command(UpdateBackingStoresCommand { move(front), move(back), front_id, back_id });
}
void RenderingThread::present_frame(Gfx::IntRect viewport_rect)
u64 RenderingThread::present_frame(Gfx::IntRect viewport_rect)
{
m_thread_data->set_needs_present(viewport_rect);
return m_thread_data->set_needs_present(viewport_rect);
}
void RenderingThread::wait_for_frame(u64 frame_id)
{
m_thread_data->wait_for_frame(frame_id);
}
void RenderingThread::request_screenshot(NonnullRefPtr<Gfx::PaintingSurface> target_surface, Function<void()>&& callback)