x11: initial implementation of from_existing_window

This adds the ability to create a glutin Window that wraps a pre-existing X
Window. The proximal motivation for this is to allow writing of XScreensaver
hacks in Rust, but it might also be useful for embedding 3D graphics in larger
applications with full process separation, etc.

This commit includes a bit of inline documentation, but no tests, and the
details of what if any WindowAttributes or pixel information should be applied
to the existing window aren't worked out.

1 files changed, 12 insertions, 3 deletions

diff --git a/src/os/unix.rs b/src/os/unix.rs
index 61c89bc..0d89571 100644
--- a/src/os/unix.rs
+++ b/src/os/unix.rs
@@ -1,5 +1,7 @@
 #![cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd", target_os = "openbsd"))]
 
+use std::os::raw::c_ulong;
+
 use libc;
 use Window;
 use platform::Window as LinuxWindow;
@@ -41,9 +43,16 @@ impl WindowExt for Window {
 }
 
 /// Additional methods on `WindowBuilder` that are specific to Unix.
-pub trait WindowBuilderExt {
-
+pub trait WindowBuilderExt<'a> {
+    fn from_existing_window(mut self, window_id: c_ulong)  -> WindowBuilder<'a>;
 }
 
-impl<'a> WindowBuilderExt for WindowBuilder<'a> {
+impl<'a> WindowBuilderExt<'a> for WindowBuilder<'a> {
+
+    /// Tells this (UNIX/X11) WindowBuilder to use an existing X window (eg,
+    /// one created by another application) instead of creating a new window.
+    fn from_existing_window(mut self, window_id: c_ulong) -> WindowBuilder<'a> {
+        self.platform_specific.existing_x11_window_id = Some(window_id);
+        self
+    }
 }