make map_async function slim and handle the other stuff inside the download_and_handle_internal fn which is only called from a seperate thread

voxygen/src/render/renderer/screenshot.rs

@@ -1,5 +1,6 @@
 use super::super::pipelines::blit;
 use common_base::prof_span;
+use crossbeam_channel;
 use tracing::error;
 
 pub type ScreenshotFn = Box<dyn FnOnce(Result<image::RgbImage, String>) + Send>;
@@ -135,6 +136,7 @@ impl TakeScreenshot {
         }
     }
 
+    /// Don't call this from the main loop, it will block for a while
     fn download_and_handle_internal(self) {
         prof_span!("download_and_handle_internal");
         // Calculate padded bytes per row
@@ -144,7 +146,22 @@ impl TakeScreenshot {
         let buffer = std::sync::Arc::new(self.buffer);
         let buffer2 = std::sync::Arc::clone(&buffer);
         let buffer_slice = buffer.slice(..);
+        let (map_result_sender, map_result_receiver) = crossbeam_channel::bounded(1);
         buffer_slice.map_async(wgpu::MapMode::Read, move |result| {
+            map_result_sender
+                .send(result)
+                .expect("seems like the receiver broke, which should not happen");
+        });
+        let result = match map_result_receiver.recv() {
+            Ok(result) => result,
+            Err(e) => {
+                error!(
+                    ?e,
+                    "map_async never send the result for the screenshot mapping"
+                );
+                return;
+            },
+        };
         let padded_buffer;
         let buffer_slice = buffer2.slice(..);
         let rows = match result {
@@ -213,13 +230,11 @@ impl TakeScreenshot {
         }
         .map(|pixel_bytes| {
             image::RgbImage::from_vec(self.width, self.height, pixel_bytes).expect(
-                    "Failed to create ImageBuffer! Buffer was not large enough. This should not \
-                     occur",
+                "Failed to create ImageBuffer! Buffer was not large enough. This should not occur",
             )
         });
         // Call supplied handler
         (self.screenshot_fn)(image);
-        });
     }
 }