Keep aspect ratio with upload previews

@@ -21,11 +21,28 @@ pub(super) async fn upload_preview_logic( mut rx_canvas :broadcast::Receiver<Dom
             let context = canvas
                         . get_context("2d").unwrap().unwrap()
                         . dyn_into::<CanvasRenderingContext2d>().unwrap();
+            let image_width = upload.bitmap().width() as f64;
+            let image_height = upload.bitmap().height() as f64;
+            let canvas_width = canvas.width() as f64;
+            let canvas_height = canvas.height() as f64;
+
+            /* scale with aspect ratio */
+            let (ox, oy, width, height) = if image_width > image_height {
+                let f = canvas_width / image_width;
+                let dest_height = image_height * f;
+                let o_y = (canvas_height - dest_height) / 2.0;
+                (0.0, o_y, canvas_width, dest_height)
+            } else {
+                let f = canvas_height / image_height;
+                let dest_width = image_width * f;
+                let o_x = (canvas_width - dest_width) / 2.0;
+                (o_x, 0.0, dest_width, canvas_height)
+            };
+
             context
                 . draw_image_with_image_bitmap_and_dw_and_dh(
                       &upload.bitmap()
-                    , 0.0, 0.0
-                    , canvas.width() as f64, canvas.height() as f64 )
+                    , ox, oy, width, height )
                 . unwrap();
         }
     }