WindowServer+LibGUI: Add a way to get notified at display refresh rate

This patch adds GUI::DisplayLink, a mechanism for registering callbacks
that will fire at the display refresh rate.

Note that we don't actually know the screen refresh rate, but this is
instead completely driven by WindowServer's compositing timer. For all
current intents and purposes it does the job well enough. :^)

1 files changed, 9 insertions, 0 deletions

diff --git a/Servers/WindowServer/Compositor.cpp b/Servers/WindowServer/Compositor.cpp
index a821855a16..e5cf24182b 100644
--- a/Servers/WindowServer/Compositor.cpp
+++ b/Servers/WindowServer/Compositor.cpp
@@ -25,6 +25,7 @@
  */
 
 #include "Compositor.h"
+#include "ClientConnection.h"
 #include "Event.h"
 #include "EventLoop.h"
 #include "Screen.h"
@@ -69,6 +70,7 @@ Compositor::Compositor()
     init_bitmaps();
 
     m_compose_timer->on_timeout = [&]() {
+        notify_display_links();
 #if defined(COMPOSITOR_DEBUG)
         dbgprintf("Compositor: delayed frame callback: %d rects\n", m_dirty_rects.size());
 #endif
@@ -466,4 +468,11 @@ void Compositor::draw_cursor()
     m_last_cursor_rect = cursor_rect;
 }
 
+void Compositor::notify_display_links()
+{
+    ClientConnection::for_each_client([](auto& client) {
+        client.notify_display_link({});
+    });
+}
+
 }