Detach wgl and win32

src/api/wgl/make_current_guard.rs

@@ -0,0 +1,47 @@
+use std::marker::PhantomData;
+use std::io;
+
+use libc;
+use winapi;
+use CreationError;
+
+use super::gl;
+/// A guard for when you want to make the context current. Destroying the guard restores the
+/// previously-current context.
+pub struct CurrentContextGuard<'a, 'b> {
+    previous_hdc: winapi::HDC,
+    previous_hglrc: winapi::HGLRC,
+    marker1: PhantomData<&'a ()>,
+    marker2: PhantomData<&'b ()>,
+}
+
+impl<'a, 'b> CurrentContextGuard<'a, 'b> {
+    pub unsafe fn make_current(hdc: winapi::HDC, context: winapi::HGLRC)
+                               -> Result<CurrentContextGuard<'a, 'b>, CreationError>
+    {
+        let previous_hdc = gl::wgl::GetCurrentDC() as winapi::HDC;
+        let previous_hglrc = gl::wgl::GetCurrentContext() as winapi::HGLRC;
+
+        let result = gl::wgl::MakeCurrent(hdc as *const _, context as *const _);
+        if result == 0 {
+            return Err(CreationError::OsError(format!("wglMakeCurrent function failed: {}",
+                                                      format!("{}", io::Error::last_os_error()))));
+        }
+
+        Ok(CurrentContextGuard {
+            previous_hdc: previous_hdc,
+            previous_hglrc: previous_hglrc,
+            marker1: PhantomData,
+            marker2: PhantomData,
+        })
+    }
+}
+
+impl<'a, 'b> Drop for CurrentContextGuard<'a, 'b> {
+    fn drop(&mut self) {
+        unsafe {
+            gl::wgl::MakeCurrent(self.previous_hdc as *const libc::c_void,
+                                 self.previous_hglrc as *const libc::c_void);
+        }
+    }
+}