render: don't require framebuffer to perform shm screencopies

src/gfx_apis/vulkan/image.rs

@@ -533,15 +533,18 @@ impl GfxFramebuffer for VulkanImage {
     }
 
     fn copy_to_shm(
-        &self,
-        _x: i32,
-        _y: i32,
-        _width: i32,
-        _height: i32,
-        _format: &Format,
-        _shm: &[Cell<u8>],
+        self: Rc<Self>,
+        x: i32,
+        y: i32,
+        width: i32,
+        height: i32,
+        stride: i32,
+        format: &'static Format,
+        shm: &[Cell<u8>],
     ) -> Result<(), GfxError> {
-        return Err(VulkanError::UnsupportedOperation.into());
+        self.renderer
+            .read_pixels(&self, x, y, width, height, stride, format, shm)
+            .map_err(|e| e.into())
     }
 
     fn format(&self) -> &'static Format {