Add x11 window capture (video and screenshot)

include/WindowSelector.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <X11/Xlib.h>
+
+#include <mglpp/graphics/Color.hpp>
+
+namespace gsr {
+    class WindowSelector {
+    public:
+        WindowSelector();
+        WindowSelector(const WindowSelector&) = delete;
+        WindowSelector& operator=(const WindowSelector&) = delete;
+        ~WindowSelector();
+
+        bool start(mgl::Color border_color);
+        void stop();
+        bool is_started() const;
+
+        bool failed() const;
+        bool poll_events();
+        bool take_selection();
+        bool take_canceled();
+        Window get_selection() const;
+    private:
+        Display *dpy = nullptr;
+        Cursor crosshair_cursor = None;
+        Colormap border_window_colormap = None;
+        Window border_window = None;
+        Window selected_window = None;
+        bool selected = false;
+        bool canceled = false;
+    };
+}