Forgot to include screen.rs earlier.

wmakerlib/src/screen.rs

@@ -0,0 +1,11 @@
+use std::ffi::c_void;
+
+pub type Screen = c_void;
+
+pub mod ffi {
+    use super::Screen;
+
+    unsafe extern "C" {
+        pub fn wScreenGetRootWin(screen: *mut Screen) -> x11::xlib::Window;
+    }
+}