gfx: add GfxBlendBuffer

src/backends/metal/present.rs

@@ -749,6 +749,7 @@ impl MetalConnector {
                         ReleaseSync::Explicit,
                         &latched.pass,
                         &latched.damage,
+                        None,
                     )
                     .map_err(MetalError::RenderFrame)?;
                 sync_file = buffer.copy_to_dev(sf)?;

src/backends/x.rs

@@ -755,6 +755,7 @@ impl XBackend {
                 ReleaseSync::Implicit,
                 &image.tex.get(),
                 true,
+                None,
             );
             if let Err(e) = res {
                 log::error!("Could not render screen: {}", ErrorFmt(e));