Flesh out glium compatibility

src/backend/glium.rs

@@ -1,9 +1,15 @@
-use backend::graphics::egl::{EGLGraphicsBackend, SwapBuffersError};
-use glium::SwapBuffersError as GliumSwapBuffersError;
-use glium::backend::Backend;
+//! Glium compatibility module
 
+use backend::graphics::egl::{EGLGraphicsBackend, SwapBuffersError};
+use glium::Frame;
+use glium::SwapBuffersError as GliumSwapBuffersError;
+use glium::backend::{Backend, Context};
+use glium::debug::DebugCallbackBehavior;
+use std::ops::Deref;
 use std::os::raw::c_void;
 
+use std::rc::Rc;
+
 impl From<SwapBuffersError> for GliumSwapBuffersError {
     fn from(error: SwapBuffersError) -> Self {
         match error {
@@ -13,19 +19,61 @@ impl From<SwapBuffersError> for GliumSwapBuffersError {
     }
 }
 
-pub struct GliumGraphicBackend<T: EGLGraphicsBackend>(T);
+/// Wrapper to expose `glium` compatibility
+pub struct GliumGraphicsBackend<T: EGLGraphicsBackend> {
+    context: Rc<Context>,
+    backend: Rc<InternalBackend<T>>,
+}
 
+struct InternalBackend<T: EGLGraphicsBackend>(T);
+
+impl<T: EGLGraphicsBackend + 'static> GliumGraphicsBackend<T> {
+    fn new(backend: T) -> GliumGraphicsBackend<T> {
+        let internal = Rc::new(InternalBackend(backend));
+
+        GliumGraphicsBackend {
+            // cannot fail
+            context: unsafe {
+                Context::new::<_, ()>(internal.clone(), false, DebugCallbackBehavior::default()).unwrap()
+            },
+            backend: internal,
+        }
+    }
+
+    /// Start drawing on the backbuffer.
+    ///
+    /// This function returns a `Frame`, which can be used to draw on it. When the `Frame` is
+    /// destroyed, the buffers are swapped.
+    ///
+    /// Note that destroying a `Frame` is immediate, even if vsync is enabled.
+    #[inline]
+    pub fn draw(&self) -> Frame {
+        Frame::new(self.context.clone(),
+                   self.backend.get_framebuffer_dimensions())
+    }
+}
+
+impl<T: EGLGraphicsBackend> Deref for GliumGraphicsBackend<T> {
+    type Target = Context;
+
+    fn deref(&self) -> &Context {
+        &self.context
+    }
+}
+
+/// Converter trait to expose `glium` compatibility for all `EGLGraphicsBackend`s
 pub trait IntoGlium: EGLGraphicsBackend + Sized {
-    fn into_glium(self) -> GliumGraphicBackend<Self>;
+    /// Wrap the given `EGLGraphicsBackend` to a `GliumGraphicBackend`
+    fn into_glium(self) -> GliumGraphicsBackend<Self>;
 }
 
-impl<T: EGLGraphicsBackend> IntoGlium for T {
-    fn into_glium(self) -> GliumGraphicBackend<Self> {
-        GliumGraphicBackend(self)
+impl<T: EGLGraphicsBackend + 'static> IntoGlium for T {
+    fn into_glium(self) -> GliumGraphicsBackend<Self> {
+        GliumGraphicsBackend::new(self)
     }
 }
 
-unsafe impl<T: EGLGraphicsBackend> Backend for GliumGraphicBackend<T> {
+unsafe impl<T: EGLGraphicsBackend> Backend for InternalBackend<T> {
     fn swap_buffers(&self) -> Result<(), GliumSwapBuffersError> {
         self.0.swap_buffers().map_err(Into::into)
     }