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, 11 insertions, 3 deletions

diff --git a/src/platform/linux/api_dispatch.rs b/src/platform/linux/api_dispatch.rs
index 54e0186..3a2a1e8 100644
--- a/src/platform/linux/api_dispatch.rs
+++ b/src/platform/linux/api_dispatch.rs
@@ -21,9 +21,14 @@ use api::x11;
 use api::x11::XConnection;
 use api::x11::XError;
 use api::x11::XNotSupported;
+use std::os::raw::c_ulong;
 
 #[derive(Clone, Default)]
-pub struct PlatformSpecificWindowBuilderAttributes;
+pub struct PlatformSpecificWindowBuilderAttributes {
+    /// Optionally tells the WindowBuilder to re-use an existing X window with
+    /// the given Window id number
+    pub existing_x11_window_id: Option<c_ulong>,
+}
 
 enum Backend {
     X(Arc<XConnection>),
@@ -175,7 +180,7 @@ impl<'a> Iterator for WaitEventsIterator<'a> {
 impl Window {
     #[inline]
     pub fn new(window: &WindowAttributes, pf_reqs: &PixelFormatRequirements,
-               opengl: &GlAttributes<&Window>, _: &PlatformSpecificWindowBuilderAttributes)
+               opengl: &GlAttributes<&Window>, platform: &PlatformSpecificWindowBuilderAttributes)
                -> Result<Window, CreationError>
     {
         match *BACKEND {
@@ -194,7 +199,10 @@ impl Window {
                     _ => panic!()       // TODO: return an error
                 });
 
-                x11::Window::new(connec, window, pf_reqs, &opengl).map(Window::X)
+                match platform.existing_x11_window_id {
+                    None => x11::Window::new(connec, window, pf_reqs, &opengl).map(Window::X),
+                    Some(window_id) => x11::Window::from_existing_window(connec, window, pf_reqs, &opengl, window_id).map(Window::X),
+                }
             },
 
             Backend::Error(ref error) => Err(CreationError::NoBackendAvailable(Box::new(error.clone())))