Echo the Create Bounding Boxes background as a UI preview

comfy_extras/nodes_bounding_boxes.py

@@ -5,6 +5,7 @@
 from PIL import Image, ImageDraw, ImageEnhance, ImageFont
 from typing_extensions import override
 
+import nodes
 from comfy_api.latest import ComfyExtension, io
 from comfy_extras.color_util import hex_to_rgb, normalize_palette, readable_color
 
@@ -361,6 +362,9 @@ def execute(cls, width, height, editor_state=None, last_incoming=None, backgroun
         ui = {"dims": [width, height]}
         if incoming:
             ui["input_bboxes"] = incoming
+        if background is not None and len(background) > 0:
+            saved = nodes.PreviewImage().save_images(background[:1], "comfy.bboxes.background")
+            ui["background_images"] = saved["ui"]["images"]
         return io.NodeOutput(
             preview,
             fractions_to_bbox_frame(regions, width, height),

tests-unit/comfy_extras_test/nodes_bounding_boxes_test.py

@@ -0,0 +1,40 @@
+import os
+
+import torch
+from PIL import Image
+
+import folder_paths
+from comfy.cli_args import args as cli_args
+
+if not torch.cuda.is_available():
+    cli_args.cpu = True
+
+from comfy_extras.nodes_bounding_boxes import CreateBoundingBoxes  # noqa: E402
+
+
+def run(background=None):
+    return CreateBoundingBoxes.execute(width=64, height=64, background=background).ui
+
+
+def test_echoes_the_first_background_image_as_a_temp_preview(tmp_path, monkeypatch):
+    monkeypatch.setattr(folder_paths, "get_temp_directory", lambda: str(tmp_path))
+    first = torch.zeros(1, 48, 80, 3)
+    second = torch.ones(1, 48, 80, 3)
+
+    ui = run(background=torch.cat([first, second]))
+
+    [entry] = ui["background_images"]
+    assert entry["type"] == "temp"
+    path = os.path.join(str(tmp_path), entry["subfolder"], entry["filename"])
+    with Image.open(path) as saved:
+        assert saved.size == (80, 48)
+        assert saved.getpixel((0, 0)) == (0, 0, 0)
+
+
+def test_omits_the_background_preview_without_a_background(tmp_path, monkeypatch):
+    monkeypatch.setattr(folder_paths, "get_temp_directory", lambda: str(tmp_path))
+
+    ui = run()
+
+    assert "background_images" not in ui
+    assert ui["dims"] == [64, 64]