feat(background_manager): option to disable pseudo-transparency

This adds a new config option to select between pseudo transparency and real transparency.

doc/config.cmake

@@ -414,6 +414,7 @@ screenchange-reload = true
 ;compositing-background = screen
 ;compositing-foreground = source
 ;compositing-border = over
+;pseudo-transparency = false
 
 [global/wm]
 margin-top = 5

include/x11/background_manager.hpp

@@ -47,9 +47,11 @@ class background_manager : public signal_receiver<SIGN_PRIORITY_SCREEN, signals:
   unique_ptr<cairo::xcb_surface> m_surface;
 
   bool m_attached{false};
+  bool m_pseudo_transparency{false};
 
-  void allocate_resources();
+  void allocate_resources(bool use_root_depth);
   void free_resources();
+  void make_transparent_pixmap();
   void fetch_root_pixmap();
 
 };

src/x11/background_manager.cpp

@@ -1,5 +1,7 @@
 #include "cairo/surface.hpp"
+#include "cairo/context.hpp"
 #include "events/signal.hpp"
+#include "components/config.hpp"
 #include "components/logger.hpp"
 #include "x11/atoms.hpp"
 #include "x11/connection.hpp"
@@ -19,6 +21,7 @@ background_manager::background_manager(
   , m_sig(sig)
   , m_log(log) {
   m_sig.attach(this);
+  m_pseudo_transparency = config::make().get("settings", "pseudo-transparency", false);
 }
 
 background_manager::~background_manager() {
@@ -40,7 +43,7 @@ void background_manager::activate(xcb_window_t window, xcb_rectangle_t rect) {
   free_resources();
 
   // make sure that we receive a notification when the background changes
-  if(!m_attached) {
+  if(!m_attached && m_pseudo_transparency) {
     m_connection.ensure_event_mask(m_connection.root(), XCB_EVENT_MASK_PROPERTY_CHANGE);
     m_connection.flush();
     m_connection.attach_sink(this, SINK_PRIORITY_SCREEN);
@@ -48,7 +51,11 @@ void background_manager::activate(xcb_window_t window, xcb_rectangle_t rect) {
 
   m_window = window;
   m_rect = rect;
-  fetch_root_pixmap();
+  if(m_pseudo_transparency) {
+    fetch_root_pixmap();
+  } else {
+    make_transparent_pixmap();
+  }
 }
 
 void background_manager::deactivate() {
@@ -56,7 +63,7 @@ void background_manager::deactivate() {
 }
 
 
-void background_manager::allocate_resources() {
+void background_manager::allocate_resources(bool use_root_depth) {
   if(!m_visual) {
     m_log.trace("background_manager: Finding root visual");
     m_visual = m_connection.visual_type_for_id(m_connection.screen(), m_connection.screen()->root_visual);
@@ -66,7 +73,8 @@ void background_manager::allocate_resources() {
   if(m_pixmap == XCB_NONE) {
     m_log.trace("background_manager: Allocating pixmap");
     m_pixmap = m_connection.generate_id();
-    m_connection.create_pixmap(m_connection.screen()->root_depth, m_pixmap, m_window, m_rect.width, m_rect.height);
+    auto depth = use_root_depth ? m_connection.screen()->root_depth : 32;
+    m_connection.create_pixmap(depth, m_pixmap, m_window, m_rect.width, m_rect.height);
   }
 
   if(m_gcontext == XCB_NONE) {
@@ -104,8 +112,17 @@ void background_manager::free_resources() {
   }
 }
 
+void background_manager::make_transparent_pixmap() {
+  allocate_resources(false);
+
+  m_log.trace("background_manager: Using transparent background pixmap");
+  auto context = cairo::context(*m_surface, m_log);
+  context << (unsigned int)0;
+}
+
 void background_manager::fetch_root_pixmap() {
-  allocate_resources();
+  allocate_resources(true);
+
   m_log.trace("background_manager: Fetching pixmap");
 
   int pixmap_depth;
@@ -135,6 +152,8 @@ void background_manager::fetch_root_pixmap() {
 }
 
 void background_manager::handle(const evt::property_notify& evt) {
+  if(!m_pseudo_transparency) return;
+
   // if region that we should observe is empty, don't do anything
   if(m_rect.width == 0 || m_rect.height == 0) return;
 
@@ -145,6 +164,8 @@ void background_manager::handle(const evt::property_notify& evt) {
 }
 
 bool background_manager::on(const signals::ui::update_geometry&) {
+  if(!m_pseudo_transparency) return false;
+
   fetch_root_pixmap();
   m_sig.emit(signals::ui::update_background());
   return false;