LibWebView+WebContent: Drive repainting from WebContent process

With this change, chrome no longer has to ask the WebContent process
to paint the next frame into a specified bitmap. Instead, it allocates
bitmaps and sends them to WebContent, which then lets chrome know when
the painting is done.

This work is a preparation to move the execution of painting commands
into a separate thread. Now, it is much easier to start working on the
next frame while the current one is still rendering. This is because
WebContent does not have to inform chrome that the current frame is
ready before it can request the next frame.

Additionally, as a side bonus, we can now eliminate the
did_invalidate_content_rect and did_change_selection IPC calls. These
were used solely for the purpose of informing chrome that it needed to
request a repaint.

Userland/Services/WebContent/ConnectionFromClient.cpp

@@ -57,7 +57,6 @@ ConnectionFromClient::ConnectionFromClient(NonnullOwnPtr<Core::LocalSocket> sock
     : IPC::ConnectionFromClient<WebContentClientEndpoint, WebContentServerEndpoint>(*this, move(socket), 1)
     , m_page_host(PageHost::create(*this))
 {
-    m_paint_flush_timer = Web::Platform::Timer::create_single_shot(0, [this] { flush_pending_paint_requests(); });
     m_input_event_queue_timer = Web::Platform::Timer::create_single_shot(0, [this] { process_next_input_event(); });
 }
 
@@ -141,44 +140,12 @@ void ConnectionFromClient::set_viewport_rect(Web::DevicePixelRect const& rect)
     page().set_viewport_rect(rect);
 }
 
-void ConnectionFromClient::add_backing_store(i32 backing_store_id, Gfx::ShareableBitmap const& bitmap)
+void ConnectionFromClient::add_backing_store(i32 front_bitmap_id, Gfx::ShareableBitmap const& front_bitmap, i32 back_bitmap_id, Gfx::ShareableBitmap const& back_bitmap)
 {
-    m_backing_stores.set(backing_store_id, *const_cast<Gfx::ShareableBitmap&>(bitmap).bitmap());
-}
-
-void ConnectionFromClient::remove_backing_store(i32 backing_store_id)
-{
-    m_backing_stores.remove(backing_store_id);
-    m_pending_paint_requests.remove_all_matching([backing_store_id](auto& pending_repaint_request) { return pending_repaint_request.bitmap_id == backing_store_id; });
-}
-
-void ConnectionFromClient::paint(Web::DevicePixelRect const& content_rect, i32 backing_store_id)
-{
-    for (auto& pending_paint : m_pending_paint_requests) {
-        if (pending_paint.bitmap_id == backing_store_id) {
-            pending_paint.content_rect = content_rect;
-            return;
-        }
-    }
-
-    auto it = m_backing_stores.find(backing_store_id);
-    if (it == m_backing_stores.end()) {
-        did_misbehave("Client requested paint with backing store ID");
-        return;
-    }
-
-    auto& bitmap = *it->value;
-    m_pending_paint_requests.append({ content_rect, bitmap, backing_store_id });
-    m_paint_flush_timer->start();
-}
-
-void ConnectionFromClient::flush_pending_paint_requests()
-{
-    for (auto& pending_paint : m_pending_paint_requests) {
-        page().paint(pending_paint.content_rect, *pending_paint.bitmap);
-        async_did_paint(pending_paint.content_rect.to_type<int>(), pending_paint.bitmap_id);
-    }
-    m_pending_paint_requests.clear();
+    m_backing_stores.front_bitmap_id = front_bitmap_id;
+    m_backing_stores.back_bitmap_id = back_bitmap_id;
+    m_backing_stores.front_bitmap = *const_cast<Gfx::ShareableBitmap&>(front_bitmap).bitmap();
+    m_backing_stores.back_bitmap = *const_cast<Gfx::ShareableBitmap&>(back_bitmap).bitmap();
 }
 
 void ConnectionFromClient::process_next_input_event()
@@ -881,7 +848,6 @@ Messages::WebContentServer::GetSelectedTextResponse ConnectionFromClient::get_se
 void ConnectionFromClient::select_all()
 {
     page().page().focused_context().select_all();
-    page().page().client().page_did_change_selection();
 }
 
 Messages::WebContentServer::DumpLayoutTreeResponse ConnectionFromClient::dump_layout_tree()

Userland/Services/WebContent/ConnectionFromClient.h

@@ -44,6 +44,8 @@ public:
     PageHost& page_host() { return *m_page_host; }
     PageHost const& page_host() const { return *m_page_host; }
 
+    auto& backing_stores() { return m_backing_stores; }
+
 private:
     explicit ConnectionFromClient(NonnullOwnPtr<Core::LocalSocket>);
 
@@ -58,7 +60,6 @@ private:
     virtual void update_screen_rects(Vector<Web::DevicePixelRect> const&, u32) override;
     virtual void load_url(URL const&) override;
     virtual void load_html(ByteString const&) override;
-    virtual void paint(Web::DevicePixelRect const&, i32) override;
     virtual void set_viewport_rect(Web::DevicePixelRect const&) override;
     virtual void mouse_down(Web::DevicePixelPoint, Web::DevicePixelPoint, unsigned, unsigned, unsigned) override;
     virtual void mouse_move(Web::DevicePixelPoint, Web::DevicePixelPoint, unsigned, unsigned, unsigned) override;
@@ -67,8 +68,7 @@ private:
     virtual void doubleclick(Web::DevicePixelPoint, Web::DevicePixelPoint, unsigned, unsigned, unsigned) override;
     virtual void key_down(i32, unsigned, u32) override;
     virtual void key_up(i32, unsigned, u32) override;
-    virtual void add_backing_store(i32, Gfx::ShareableBitmap const&) override;
-    virtual void remove_backing_store(i32) override;
+    virtual void add_backing_store(i32 front_bitmap_id, Gfx::ShareableBitmap const& front_bitmap, i32 back_bitmap_id, Gfx::ShareableBitmap const& back_bitmap) override;
     virtual void debug_request(ByteString const&, ByteString const&) override;
     virtual void get_source() override;
     virtual void inspect_dom_tree() override;
@@ -132,20 +132,17 @@ private:
     virtual Messages::WebContentServer::GetSelectedTextResponse get_selected_text() override;
     virtual void select_all() override;
 
-    void flush_pending_paint_requests();
-
     void report_finished_handling_input_event(bool event_was_handled);
 
     NonnullOwnPtr<PageHost> m_page_host;
-    struct PaintRequest {
-        Web::DevicePixelRect content_rect;
-        NonnullRefPtr<Gfx::Bitmap> bitmap;
-        i32 bitmap_id { -1 };
-    };
-    Vector<PaintRequest> m_pending_paint_requests;
-    RefPtr<Web::Platform::Timer> m_paint_flush_timer;
 
-    HashMap<i32, NonnullRefPtr<Gfx::Bitmap>> m_backing_stores;
+    struct BackingStores {
+        i32 front_bitmap_id { -1 };
+        i32 back_bitmap_id { -1 };
+        RefPtr<Gfx::Bitmap> front_bitmap;
+        RefPtr<Gfx::Bitmap> back_bitmap;
+    };
+    BackingStores m_backing_stores;
 
     HashMap<Web::DOM::Document*, NonnullOwnPtr<WebContentConsoleClient>> m_console_clients;
     WeakPtr<WebContentConsoleClient> m_top_level_document_console_client;

Userland/Services/WebContent/PageClient.cpp

@@ -51,9 +51,21 @@ PageClient::PageClient(PageHost& owner, u64 id)
     , m_id(id)
 {
     setup_palette();
-    m_invalidation_coalescing_timer = Web::Platform::Timer::create_single_shot(0, [this] {
-        client().async_did_invalidate_content_rect({ m_invalidation_rect.x().value(), m_invalidation_rect.y().value(), m_invalidation_rect.width().value(), m_invalidation_rect.height().value() });
-        m_invalidation_rect = {};
+
+    m_repaint_timer = Web::Platform::Timer::create_single_shot(0, [this] {
+        if (!client().backing_stores().back_bitmap) {
+            warnln("Skip painting because back bitmap is not initialized");
+            return;
+        }
+
+        auto& back_bitmap = *client().backing_stores().back_bitmap;
+        auto viewport_rect = page().css_to_device_rect(page().top_level_traversable()->viewport_rect());
+        paint(viewport_rect, back_bitmap);
+
+        auto& backing_stores = client().backing_stores();
+        swap(backing_stores.front_bitmap, backing_stores.back_bitmap);
+        swap(backing_stores.front_bitmap_id, backing_stores.back_bitmap_id);
+        client().did_paint(viewport_rect.to_type<int>(), backing_stores.front_bitmap_id);
     });
 
 #ifdef HAS_ACCELERATED_GRAPHICS
@@ -63,6 +75,12 @@ PageClient::PageClient(PageHost& owner, u64 id)
 #endif
 }
 
+void PageClient::schedule_repaint()
+{
+    if (!m_repaint_timer->is_active())
+        m_repaint_timer->start();
+}
+
 void PageClient::visit_edges(JS::Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
@@ -194,18 +212,12 @@ void PageClient::paint(Web::DevicePixelRect const& content_rect, Gfx::Bitmap& ta
 void PageClient::set_viewport_rect(Web::DevicePixelRect const& rect)
 {
     page().top_level_traversable()->set_viewport_rect(page().device_to_css_rect(rect));
+    schedule_repaint();
 }
 
-void PageClient::page_did_invalidate(Web::CSSPixelRect const& content_rect)
+void PageClient::page_did_invalidate(Web::CSSPixelRect const&)
 {
-    m_invalidation_rect = m_invalidation_rect.united(page().enclosing_device_rect(content_rect));
-    if (!m_invalidation_coalescing_timer->is_active())
-        m_invalidation_coalescing_timer->start();
-}
-
-void PageClient::page_did_change_selection()
-{
-    client().async_did_change_selection();
+    schedule_repaint();
 }
 
 void PageClient::page_did_request_cursor_change(Gfx::StandardCursor cursor)

Userland/Services/WebContent/PageClient.h

@@ -28,6 +28,8 @@ public:
 
     static void set_use_gpu_painter();
 
+    void schedule_repaint();
+
     virtual Web::Page& page() override { return *m_page; }
     virtual Web::Page const& page() const override { return *m_page; }
 
@@ -75,7 +77,6 @@ private:
     virtual double device_pixels_per_css_pixel() const override { return m_device_pixels_per_css_pixel; }
     virtual Web::CSS::PreferredColorScheme preferred_color_scheme() const override { return m_preferred_color_scheme; }
     virtual void page_did_invalidate(Web::CSSPixelRect const&) override;
-    virtual void page_did_change_selection() override;
     virtual void page_did_request_cursor_change(Gfx::StandardCursor) override;
     virtual void page_did_layout() override;
     virtual void page_did_change_title(ByteString const&) override;
@@ -148,8 +149,8 @@ private:
     bool m_should_show_line_box_borders { false };
     bool m_has_focus { false };
 
-    RefPtr<Web::Platform::Timer> m_invalidation_coalescing_timer;
-    Web::DevicePixelRect m_invalidation_rect;
+    RefPtr<Web::Platform::Timer> m_repaint_timer;
+
     Web::CSS::PreferredColorScheme m_preferred_color_scheme { Web::CSS::PreferredColorScheme::Auto };
 
     RefPtr<WebDriverConnection> m_webdriver;

Userland/Services/WebContent/WebContentClient.ipc

@@ -17,9 +17,7 @@ endpoint WebContentClient
     did_request_navigate_back() =|
     did_request_navigate_forward() =|
     did_request_refresh() =|
-    did_paint(Gfx::IntRect content_rect, i32 bitmap_id) =|
-    did_invalidate_content_rect(Gfx::IntRect content_rect) =|
-    did_change_selection() =|
+    did_paint(Gfx::IntRect content_rect, i32 bitmap_id) => ()
     did_request_cursor_change(i32 cursor_type) =|
     did_layout(Gfx::IntSize content_size) =|
     did_change_title(ByteString title) =|

Userland/Services/WebContent/WebContentServer.ipc

@@ -22,10 +22,8 @@ endpoint WebContentServer
     load_url(URL url) =|
     load_html(ByteString html) =|
 
-    add_backing_store(i32 backing_store_id, Gfx::ShareableBitmap bitmap) =|
-    remove_backing_store(i32 backing_store_id) =|
+    add_backing_store(i32 front_bitmap_id, Gfx::ShareableBitmap front_bitmap, i32 back_bitmap_id, Gfx::ShareableBitmap back_bitmap) =|
 
-    paint(Web::DevicePixelRect content_rect, i32 backing_store_id) =|
     set_viewport_rect(Web::DevicePixelRect rect) =|
 
     mouse_down(Web::DevicePixelPoint position, Web::DevicePixelPoint screen_position, unsigned button, unsigned buttons, unsigned modifiers) =|