Enable alpha blending

Author: Alan Jeffrey

webxr/glwindow/mod.rs

@@ -436,6 +436,14 @@ impl GlWindowDevice {
             (gl::NO_ERROR, gl::FRAMEBUFFER_COMPLETE)
         );
 
+        gl.enable(gl::BLEND);
+        gl.blend_func_separate(
+            gl::SRC_ALPHA,
+            gl::ONE_MINUS_SRC_ALPHA,
+            gl::ONE,
+            gl::ONE_MINUS_SRC_ALPHA,
+        );
+
         let swap_chains = SwapChains::new();
         let layer_manager = None;