WindowServer: Support windows with alpha channels. And per-WSWindow opacity.

This patch also adds a Format concept to GraphicsBitmap. For now there are
only two formats: RGB32 and RGBA32. Windows with alpha channel have their
backing stores created in the RGBA32 format.

Use this to make Terminal windows semi-transparent for that comfy rice look.
There is one problem here, in that window compositing overdraw incurs
multiple passes of blending of the same pixels. This leads to a mismatch in
opacity which is obviously not good. I will work on this in a later patch.

The alpha blending is currently straight C++. It should be relatively easy
to optimize this using SSE instructions.

For now I'm just happy with the cute effect. :^)

8 files changed, 86 insertions, 21 deletions

diff --git a/WindowServer/WSAPITypes.h b/WindowServer/WSAPITypes.h
index 8f9257c715..3ed1b55077 100644
--- a/WindowServer/WSAPITypes.h
+++ b/WindowServer/WSAPITypes.h
@@ -117,6 +117,7 @@ struct WSAPI_ServerMessage {
             size_t bpp;
             size_t pitch;
             int shared_buffer_id;
+            bool has_alpha_channel;
         } backing;
     };
 };
@@ -142,6 +143,7 @@ struct WSAPI_ClientMessage {
         DidFinishPainting,
         GetWindowBackingStore,
         SetGlobalCursorTracking,
+        SetWindowOpacity,
     };
     Type type { Invalid };
     int window_id { -1 };
@@ -157,6 +159,8 @@ struct WSAPI_ClientMessage {
         } menu;
         struct {
             WSAPI_Rect rect;
+            bool has_alpha_channel;
+            float opacity;
         } window;
     };
 };
diff --git a/WindowServer/WSClientConnection.cpp b/WindowServer/WSClientConnection.cpp
index 841d58a7c9..ad11034333 100644
--- a/WindowServer/WSClientConnection.cpp
+++ b/WindowServer/WSClientConnection.cpp
@@ -79,14 +79,14 @@ void WSClientConnection::post_message(const WSAPI_ServerMessage& message)
     ASSERT(nwritten == sizeof(message));
 }
 
-RetainPtr<GraphicsBitmap> WSClientConnection::create_shared_bitmap(const Size& size)
+RetainPtr<GraphicsBitmap> WSClientConnection::create_shared_bitmap(GraphicsBitmap::Format format, const Size& size)
 {
     RGBA32* buffer;
     int shared_buffer_id = create_shared_buffer(m_pid, size.area() * sizeof(RGBA32), (void**)&buffer);
     ASSERT(shared_buffer_id >= 0);
     ASSERT(buffer);
     ASSERT(buffer != (void*)-1);
-    return GraphicsBitmap::create_with_shared_buffer(shared_buffer_id, size, buffer);
+    return GraphicsBitmap::create_with_shared_buffer(format, shared_buffer_id, size, buffer);
 }
 
 void WSClientConnection::on_message(WSMessage& message)
@@ -236,6 +236,18 @@ void WSClientConnection::handle_request(WSAPIAddMenuSeparatorRequest& request)
     post_message(response);
 }
 
+void WSClientConnection::handle_request(WSAPISetWindowOpacityRequest& request)
+{
+    int window_id = request.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        post_error("Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    window.set_opacity(request.opacity());
+}
+
 void WSClientConnection::handle_request(WSAPISetWindowTitleRequest& request)
 {
     int window_id = request.window_id();
@@ -298,8 +310,10 @@ void WSClientConnection::handle_request(WSAPICreateWindowRequest& request)
 {
     int window_id = m_next_window_id++;
     auto window = make<WSWindow>(*this, window_id);
+    window->set_has_alpha_channel(request.has_alpha_channel());
     window->set_title(request.title());
     window->set_rect(request.rect());
+    window->set_opacity(request.opacity());
     m_windows.set(window_id, move(window));
     WSAPI_ServerMessage response;
     response.type = WSAPI_ServerMessage::Type::DidCreateWindow;
@@ -364,6 +378,7 @@ void WSClientConnection::handle_request(WSAPIGetWindowBackingStoreRequest& reque
     response.backing.bpp = sizeof(RGBA32);
     response.backing.pitch = backing_store->pitch();
     response.backing.size = backing_store->size();
+    response.backing.has_alpha_channel = backing_store->has_alpha_channel();
     response.backing.shared_buffer_id = backing_store->shared_buffer_id();
     post_message(response);
 }
@@ -419,6 +434,8 @@ void WSClientConnection::on_request(WSAPIClientRequest& request)
         return handle_request(static_cast<WSAPIGetWindowBackingStoreRequest&>(request));
     case WSMessage::APISetGlobalCursorTrackingRequest:
         return handle_request(static_cast<WSAPISetGlobalCursorTrackingRequest&>(request));
+    case WSMessage::APISetWindowOpacityRequest:
+        return handle_request(static_cast<WSAPISetWindowOpacityRequest&>(request));
     default:
         break;
     }
diff --git a/WindowServer/WSClientConnection.h b/WindowServer/WSClientConnection.h
index f2467c14fd..fdcc27adab 100644
--- a/WindowServer/WSClientConnection.h
+++ b/WindowServer/WSClientConnection.h
@@ -22,7 +22,7 @@ public:
     static void for_each_client(Function<void(WSClientConnection&)>);
 
     void post_message(const WSAPI_ServerMessage&);
-    RetainPtr<GraphicsBitmap> create_shared_bitmap(const Size&);
+    RetainPtr<GraphicsBitmap> create_shared_bitmap(GraphicsBitmap::Format, const Size&);
 
     int client_id() const { return m_client_id; }
     WSMenuBar* app_menubar() { return m_app_menubar.ptr(); }
@@ -52,6 +52,7 @@ private:
     void handle_request(WSAPIDidFinishPaintingNotification&);
     void handle_request(WSAPIGetWindowBackingStoreRequest&);
     void handle_request(WSAPISetGlobalCursorTrackingRequest&);
+    void handle_request(WSAPISetWindowOpacityRequest&);
 
     void post_error(const String&);
 
diff --git a/WindowServer/WSMessage.h b/WindowServer/WSMessage.h
index fdbd67dbe3..0656bc4bd5 100644
--- a/WindowServer/WSMessage.h
+++ b/WindowServer/WSMessage.h
@@ -39,6 +39,7 @@ public:
         APIDidFinishPaintingNotification,
         APIGetWindowBackingStoreRequest,
         APISetGlobalCursorTrackingRequest,
+        APISetWindowOpacityRequest,
         __End_API_Client_Requests,
     };
 
@@ -253,6 +254,26 @@ private:
     int m_window_id { 0 };
 };
 
+class WSAPISetWindowOpacityRequest final : public WSAPIClientRequest {
+public:
+    explicit WSAPISetWindowOpacityRequest(int client_id, int window_id, float opacity)
+        : WSAPIClientRequest(WSMessage::APISetWindowOpacityRequest, client_id)
+        , m_client_id(client_id)
+        , m_window_id(window_id)
+        , m_opacity(opacity)
+    {
+    }
+
+    int client_id() const { return m_client_id; }
+    int window_id() const { return m_window_id; }
+    float opacity() const { return m_opacity; }
+
+private:
+    int m_client_id { 0 };
+    int m_window_id { 0 };
+    float m_opacity { 0 };
+};
+
 class WSAPISetWindowRectRequest final : public WSAPIClientRequest {
 public:
     explicit WSAPISetWindowRectRequest(int client_id, int window_id, const Rect& rect)
@@ -292,19 +313,25 @@ private:
 
 class WSAPICreateWindowRequest : public WSAPIClientRequest {
 public:
-    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title)
+    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title, bool has_alpha_channel, float opacity)
         : WSAPIClientRequest(WSMessage::APICreateWindowRequest, client_id)
         , m_rect(rect)
         , m_title(title)
+        , m_opacity(opacity)
+        , m_has_alpha_channel(has_alpha_channel)
     {
     }
 
     Rect rect() const { return m_rect; }
     String title() const { return m_title; }
+    bool has_alpha_channel() const { return m_has_alpha_channel; }
+    float opacity() const { return m_opacity; }
 
 private:
     Rect m_rect;
     String m_title;
+    float m_opacity { 0 };
+    bool m_has_alpha_channel { false };
 };
 
 class WSAPIDestroyWindowRequest : public WSAPIClientRequest {
diff --git a/WindowServer/WSMessageLoop.cpp b/WindowServer/WSMessageLoop.cpp
index 6cf92b8374..199222a4dd 100644
--- a/WindowServer/WSMessageLoop.cpp
+++ b/WindowServer/WSMessageLoop.cpp
@@ -302,7 +302,7 @@ void WSMessageLoop::on_receive_from_client(int client_id, const WSAPI_ClientMess
         break;
     case WSAPI_ClientMessage::Type::CreateWindow:
         ASSERT(message.text_length < sizeof(message.text));
-        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length)));
+        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length), message.window.has_alpha_channel, message.window.opacity));
         break;
     case WSAPI_ClientMessage::Type::DestroyWindow:
         post_message(client, make<WSAPIDestroyWindowRequest>(client_id, message.window_id));
diff --git a/WindowServer/WSWindow.cpp b/WindowServer/WSWindow.cpp
index 8e440e1ec8..61e9073123 100644
--- a/WindowServer/WSWindow.cpp
+++ b/WindowServer/WSWindow.cpp
@@ -44,9 +44,10 @@ void WSWindow::set_rect(const Rect& rect)
     m_rect = rect;
     if (!m_backing || old_rect.size() != rect.size()) {
         if (m_menu)
-            m_backing = GraphicsBitmap::create(m_rect.size());
-        else if (m_client)
-            m_backing = m_client->create_shared_bitmap(m_rect.size());
+            m_backing = GraphicsBitmap::create(GraphicsBitmap::Format::RGB32, m_rect.size());
+        else if (m_client) {
+            m_backing = m_client->create_shared_bitmap(m_has_alpha_channel ? GraphicsBitmap::Format::RGBA32 : GraphicsBitmap::Format::RGB32, m_rect.size());
+        }
 
     }
     WSWindowManager::the().notify_rect_changed(*this, old_rect, rect);
diff --git a/WindowServer/WSWindow.h b/WindowServer/WSWindow.h
index 050ec7f63f..3cb02b5a35 100644
--- a/WindowServer/WSWindow.h
+++ b/WindowServer/WSWindow.h
@@ -25,6 +25,9 @@ public:
     String title() const { return m_title; }
     void set_title(String&&);
 
+    float opacity() const { return m_opacity; }
+    void set_opacity(float opacity) { m_opacity = opacity; }
+
     int x() const { return m_rect.x(); }
     int y() const { return m_rect.y(); }
     int width() const { return m_rect.width(); }
@@ -59,6 +62,9 @@ public:
     void set_global_cursor_tracking_enabled(bool);
     bool global_cursor_tracking() const { return m_global_cursor_tracking_enabled; }
 
+    bool has_alpha_channel() const { return m_has_alpha_channel; }
+    void set_has_alpha_channel(bool value) { m_has_alpha_channel = value; }
+
     // For InlineLinkedList.
     // FIXME: Maybe make a ListHashSet and then WSWindowManager can just use that.
     WSWindow* m_next { nullptr };
@@ -72,9 +78,9 @@ private:
     bool m_is_being_dragged { false };
     bool m_global_cursor_tracking_enabled { false };
     bool m_visible { true };
-
+    bool m_has_alpha_channel { false };
     WSMenu* m_menu { nullptr };
-
     RetainPtr<GraphicsBitmap> m_backing;
     int m_window_id { -1 };
+    float m_opacity { 1 };
 };
diff --git a/WindowServer/WSWindowManager.cpp b/WindowServer/WSWindowManager.cpp
index 1772a68346..02154287ef 100644
--- a/WindowServer/WSWindowManager.cpp
+++ b/WindowServer/WSWindowManager.cpp
@@ -144,8 +144,8 @@ WSWindowManager::WSWindowManager()
     (void)m_flush_count;
 #endif
     auto size = m_screen_rect.size();
-    m_front_bitmap = GraphicsBitmap::create_wrapper(size, m_screen.scanline(0));
-    m_back_bitmap = GraphicsBitmap::create_wrapper(size, m_screen.scanline(size.height()));
+    m_front_bitmap = GraphicsBitmap::create_wrapper(GraphicsBitmap::Format::RGB32, size, m_screen.scanline(0));
+    m_back_bitmap = GraphicsBitmap::create_wrapper(GraphicsBitmap::Format::RGB32, size, m_screen.scanline(size.height()));
 
     m_front_painter = make<Painter>(*m_front_bitmap);
     m_back_painter = make<Painter>(*m_back_bitmap);
@@ -170,17 +170,17 @@ WSWindowManager::WSWindowManager()
     m_cursor_bitmap_outer = CharacterBitmap::create_from_ascii(cursor_bitmap_outer_ascii, 12, 17);
 
     m_wallpaper_path = "/res/wallpapers/cool.rgb";
-    m_wallpaper = GraphicsBitmap::load_from_file(m_wallpaper_path, { 1024, 768 });
+    m_wallpaper = GraphicsBitmap::load_from_file(GraphicsBitmap::Format::RGBA32, m_wallpaper_path, { 1024, 768 });
 
 #ifdef KERNEL
     ProcFS::the().add_sys_bool("wm_flash_flush", m_flash_flush);
     ProcFS::the().add_sys_string("wm_wallpaper", m_wallpaper_path, [this] {
-        m_wallpaper = GraphicsBitmap::load_from_file(m_wallpaper_path, m_screen_rect.size());
+        m_wallpaper = GraphicsBitmap::load_from_file(GraphicsBitmap::Format::RGBA32, m_wallpaper_path, m_screen_rect.size());
         invalidate(m_screen_rect);
     });
 #endif
 
-    m_menu_selection_color = Color(0x84351a);
+    m_menu_selection_color = Color::from_rgb(0x84351a);
 
     {
         byte system_menu_name[] = { 0xf8, 0 };
@@ -242,8 +242,8 @@ void WSWindowManager::set_resolution(int width, int height)
         return;
     m_screen.set_resolution(width, height);
     m_screen_rect = m_screen.rect();
-    m_front_bitmap = GraphicsBitmap::create_wrapper({ width, height }, m_screen.scanline(0));
-    m_back_bitmap = GraphicsBitmap::create_wrapper({ width, height }, m_screen.scanline(height));
+    m_front_bitmap = GraphicsBitmap::create_wrapper(GraphicsBitmap::Format::RGB32, { width, height }, m_screen.scanline(0));
+    m_back_bitmap = GraphicsBitmap::create_wrapper(GraphicsBitmap::Format::RGB32, { width, height }, m_screen.scanline(height));
     m_front_painter = make<Painter>(*m_front_bitmap);
     m_back_painter = make<Painter>(*m_back_bitmap);
     m_buffers_are_flipped = false;
@@ -620,10 +620,17 @@ void WSWindowManager::compose()
     dbgprintf("[WM] compose #%u (%u rects)\n", ++m_compose_count, dirty_rects.size());
 #endif
 
-    auto any_window_contains_rect = [this] (const Rect& r) {
+    auto any_opaque_window_contains_rect = [this] (const Rect& r) {
         for (auto* window = m_windows_in_order.head(); window; window = window->next()) {
             if (!window->is_visible())
                 continue;
+            if (window->opacity() < 1.0f)
+                continue;
+            if (window->has_alpha_channel()) {
+                // FIXME: Just because the window has an alpha channel doesn't mean it's not opaque.
+                //        Maybe there's some way we could know this?
+                continue;
+            }
             if (outer_window_rect(window->rect()).contains(r))
                 return true;
         }
@@ -640,9 +647,8 @@ void WSWindowManager::compose()
     };
 
     for (auto& dirty_rect : dirty_rects) {
-        if (any_window_contains_rect(dirty_rect)) {
+        if (any_opaque_window_contains_rect(dirty_rect))
             continue;
-        }
         if (!m_wallpaper)
             m_back_painter->fill_rect(dirty_rect, m_background_color);
         else
@@ -665,7 +671,10 @@ void WSWindowManager::compose()
             dirty_rect_in_window_coordinates.set_y(dirty_rect_in_window_coordinates.y() - window.y());
             auto dst = window.position();
             dst.move_by(dirty_rect_in_window_coordinates.location());
-            m_back_painter->blit(dst, *backing, dirty_rect_in_window_coordinates);
+            if (window.opacity() == 1.0f)
+                m_back_painter->blit(dst, *backing, dirty_rect_in_window_coordinates);
+            else
+                m_back_painter->blit_with_opacity(dst, *backing, dirty_rect_in_window_coordinates, window.opacity());
             m_back_painter->clear_clip_rect();
         }
         m_back_painter->clear_clip_rect();