Do some cleanup and fix swap trait impls

Oops! The argument to `gfxScreenSwapBuffers` is gfxScreen_t, not
gfx3dSide_t ! Unfortunately they are both alias to libc::c_uint so we
didn't get any help from the Rust compiler when passing the screen side
into this function.

ctru-rs/examples/gfx-3d-mode.rs

@@ -62,8 +62,7 @@ fn main() {
             buf.copy_from(IMAGE.as_ptr(), IMAGE.len());
         }
 
-        drop(left);
-        drop(right);
+        drop((left, right));
 
         top_screen.flush_buffers();
         top_screen.swap_buffers();

ctru-rs/src/services/gfx.rs

@@ -81,20 +81,32 @@ pub struct TopScreen3D<'top_screen> {
 }
 
 pub trait Swap: private::Sealed {
+    /// Swaps the video buffers.
+    ///
+    /// This should be used even if double buffering is disabled.
     fn swap_buffers(&mut self);
 }
 
-trait SwappableScreen: Screen {}
-impl SwappableScreen for TopScreen {}
-impl SwappableScreen for BottomScreen {}
+impl Swap for TopScreen3D<'_> {
+    fn swap_buffers(&mut self) {
+        unsafe {
+            ctru_sys::gfxScreenSwapBuffers(ctru_sys::GFX_TOP, true);
+        }
+    }
+}
 
-impl<S: SwappableScreen> Swap for S {
-    /// Swaps the video buffers.
-    ///
-    /// This should be used even if double buffering is disabled.
+impl Swap for TopScreen {
+    fn swap_buffers(&mut self) {
+        unsafe {
+            ctru_sys::gfxScreenSwapBuffers(ctru_sys::GFX_TOP, false);
+        }
+    }
+}
+
+impl Swap for BottomScreen {
     fn swap_buffers(&mut self) {
         unsafe {
-            ctru_sys::gfxScreenSwapBuffers(self.side().into(), false);
+            ctru_sys::gfxScreenSwapBuffers(ctru_sys::GFX_BOTTOM, false);
         }
     }
 }
@@ -124,23 +136,6 @@ impl<S: FlushableScreen> Flush for S {
     }
 }
 
-impl Swap for TopScreen3D<'_> {
-    fn swap_buffers(&mut self) {
-        unsafe {
-            ctru_sys::gfxScreenSwapBuffers(Side::Left.into(), true);
-        }
-    }
-}
-
-impl TopScreen3D<'_> {
-    /// Flush the buffers for both the left and right sides of the screen.
-    pub fn flush_buffers(&mut self) {
-        let (mut left, mut right) = self.split_mut();
-        left.flush_buffer();
-        right.flush_buffer();
-    }
-}
-
 /// The left side of the top screen, when using 3D mode.
 #[derive(Debug)]
 #[non_exhaustive]
@@ -253,6 +248,13 @@ impl TopScreen3D<'_> {
             (&mut screen.left as _, &mut screen.right as _)
         })
     }
+
+    /// Convenient helper to flush the buffers for both the left and right sides of the screen.
+    pub fn flush_buffers(&mut self) {
+        let (mut left, mut right) = self.split_mut();
+        left.flush_buffer();
+        right.flush_buffer();
+    }
 }
 
 impl<'top_screen> From<&'top_screen RefCell<TopScreen>> for TopScreen3D<'top_screen> {
@@ -296,7 +298,7 @@ impl TopScreen {
 
 impl Screen for TopScreen {
     fn as_raw(&self) -> ctru_sys::gfxScreen_t {
-        self.left.as_raw()
+        ctru_sys::GFX_TOP
     }
 
     fn side(&self) -> Side {