Make app compatible with Gradio 6 (Space) and 4.x (local)

- Drop show_download_button from Gallery/Image (removed in Gradio 6; download shown by default)
- Move NVIDIA-green theme to launch() on Gradio 6, keep on Blocks for <6
- Version-detect via gr.__version__ to support both

app.py

@@ -402,7 +402,7 @@ def generate(
     )
 
 
-def build_demo() -> gr.Blocks:
+def make_theme() -> gr.themes.Base:
     nvidia_green = gr.themes.Color(
         c50="#f3f9e6",
         c100="#e3f1c2",
@@ -416,8 +416,19 @@ def build_demo() -> gr.Blocks:
         c900="#2a4200",
         c950="#1a2900",
     )
-    theme = gr.themes.Soft(primary_hue=nvidia_green, secondary_hue=nvidia_green)
-    with gr.Blocks(title="Nemotron Labs Diffusion Image", theme=theme) as demo:
+    return gr.themes.Soft(primary_hue=nvidia_green, secondary_hue=nvidia_green)
+
+
+# Gradio 6.0 moved `theme` from Blocks(...) to launch(...).
+_GRADIO_MAJOR = int(gr.__version__.split(".")[0])
+
+
+def build_demo() -> gr.Blocks:
+    theme = make_theme()
+    blocks_kwargs: dict[str, Any] = {"title": "Nemotron Labs Diffusion Image"}
+    if _GRADIO_MAJOR < 6:
+        blocks_kwargs["theme"] = theme
+    with gr.Blocks(**blocks_kwargs) as demo:
         gr.Markdown(
             "# Nemotron Labs Diffusion Image\n\n"
             "NL-Diffusion-Image generates high-resolution images via **masked discrete diffusion** "
@@ -547,9 +558,7 @@ def build_demo() -> gr.Blocks:
                 columns=3,
                 height="auto",
                 object_fit="contain",
-                show_label=False,
-                show_download_button=True,
-            )
+                show_label=False,            )
 
             gr.Markdown(
                 "### Generation speed\n\n"
@@ -560,9 +569,7 @@ def build_demo() -> gr.Blocks:
             gr.Image(
                 value=_asset("speed_comparison.gif"),
                 show_label=False,
-                interactive=False,
-                show_download_button=True,
-            )
+                interactive=False,            )
 
             with gr.Row(equal_height=True):
                 with gr.Column(scale=1):
@@ -577,9 +584,7 @@ def build_demo() -> gr.Blocks:
                     gr.Image(
                         value=_asset("architecture.png"),
                         show_label=False,
-                        interactive=False,
-                        show_download_button=True,
-                    )
+                        interactive=False,                    )
 
             with gr.Row(equal_height=True):
                 with gr.Column(scale=1):
@@ -593,9 +598,7 @@ def build_demo() -> gr.Blocks:
                     gr.Image(
                         value=_asset("benchmarks.png"),
                         show_label=False,
-                        interactive=False,
-                        show_download_button=True,
-                    )
+                        interactive=False,                    )
 
             gr.Markdown("### Key findings")
 
@@ -610,9 +613,7 @@ def build_demo() -> gr.Blocks:
                     gr.Image(
                         value=_asset("token_editing.png"),
                         show_label=False,
-                        interactive=False,
-                        show_download_button=True,
-                    )
+                        interactive=False,                    )
 
             with gr.Row(equal_height=True):
                 with gr.Column(scale=1):
@@ -627,9 +628,7 @@ def build_demo() -> gr.Blocks:
                     gr.Image(
                         value=_asset("gce_objective.png"),
                         show_label=False,
-                        interactive=False,
-                        show_download_button=True,
-                    )
+                        interactive=False,                    )
 
             with gr.Row(equal_height=True):
                 with gr.Column(scale=1):
@@ -643,9 +642,7 @@ def build_demo() -> gr.Blocks:
                     gr.Image(
                         value=_asset("few_step_generation.png"),
                         show_label=False,
-                        interactive=False,
-                        show_download_button=True,
-                    )
+                        interactive=False,                    )
 
             gr.Markdown(
                 "**Future work:** extend the model to unified vision generation and understanding."
@@ -657,7 +654,10 @@ def build_demo() -> gr.Blocks:
 demo = build_demo()
 
 if __name__ == "__main__":
-    demo.queue(default_concurrency_limit=1).launch(
-        server_name=os.getenv("HOST", "0.0.0.0"),
-        server_port=int(os.getenv("PORT", "7860")),
-    )
+    launch_kwargs: dict[str, Any] = {
+        "server_name": os.getenv("HOST", "0.0.0.0"),
+        "server_port": int(os.getenv("PORT", "7860")),
+    }
+    if _GRADIO_MAJOR >= 6:
+        launch_kwargs["theme"] = make_theme()
+    demo.queue(default_concurrency_limit=1).launch(**launch_kwargs)