Keep backgrounds separate and prevent player trails

app.py

@@ -108,6 +108,7 @@ FREE_IMAGE_STEPS = int(os.environ.get("FREE_IMAGE_STEPS", "5"))
 USE_HF_PROMPT_PROVIDER = os.environ.get("USE_HF_PROMPT_PROVIDER", "0") == "1"
 USE_HF_IMAGE_PROVIDER = os.environ.get("USE_HF_IMAGE_PROVIDER", "0") == "1"
 USE_DIFFUSION_FOR_SPRITES = os.environ.get("USE_DIFFUSION_FOR_SPRITES", "0") == "1"
+USE_DIFFUSION_FOR_BACKGROUNDS = os.environ.get("USE_DIFFUSION_FOR_BACKGROUNDS", "0") == "1"
 HF_IMAGE_MODEL = os.environ.get("HF_IMAGE_MODEL", "black-forest-labs/FLUX.1-schnell")
 HF_PROMPT_MODEL = os.environ.get("HF_PROMPT_MODEL", "Qwen/Qwen2.5-Coder-7B-Instruct:fastest")
 HF_PROMPT_ENDPOINT = os.environ.get("HF_PROMPT_ENDPOINT", "https://router.huggingface.co/v1/chat/completions")
@@ -202,7 +203,8 @@ def build_asset_prompt(role: str, prompt: str, style_hint: str) -> str:
     if is_background:
         asset_instruction = (
             "Create one complete 2D game background scene, not a texture tile, not a material sample, "
-            "not a UV map. Full scene composition for a canvas game."
+            "not a UV map. Full scene composition for a canvas game. Empty environment only: no player, "
+            "no character, no creature, no vehicle, no mascot, no foreground subject."
         )
     else:
         asset_instruction = (
@@ -1062,7 +1064,8 @@ def free_diffusion_png(spec: AssetSpec, index: int, run_id: int) -> tuple[bytes
         negative_prompt = (
             "texture map, material texture, seamless texture, tiled pattern, uv map, uv unwrap, "
             "skin texture, 3d model texture, normal map, roughness map, diffuse map, sprite sheet, "
-            "atlas, multiple objects, cropped subject, close-up surface, fabric swatch, text, watermark"
+            "atlas, multiple objects, cropped subject, close-up surface, fabric swatch, text, watermark, "
+            "person, character, player, hero, creature, monster, vehicle, mascot, foreground subject"
         )
         image = FREE_DIFFUSION_PIPE(
             spec.prompt,
@@ -1114,6 +1117,14 @@ def generate_asset(spec: AssetSpec, index: int, run_id: int) -> tuple[str, str,
             None,
             "shape-aware 2D sprite generator",
         )
+    if is_background_spec(spec) and not USE_DIFFUSION_FOR_BACKGROUNDS:
+        png_content = local_asset_png(spec, index, run_id)
+        return (
+            png_bytes_to_data_uri(png_content),
+            write_gallery_image(png_content, spec.role),
+            None,
+            "scene-safe 2D background generator",
+        )
 
     png_content, free_error = free_diffusion_png(spec, index, run_id)
     source = FREE_IMAGE_MODEL
@@ -1244,7 +1255,15 @@ def embed_assets(html_code: str, assets: dict[str, str], specs: list[AssetSpec])
           var current = image.getAttribute("src") || image.src || "";
           var mapped = pickAsset(current);
           if (mapped && mapped !== current) image.src = mapped;
-          if (!image.complete || image.naturalWidth === 0 || image.naturalHeight === 0) return;
+          if (!image.complete || image.naturalWidth === 0 || image.naturalHeight === 0) {{
+            var looksLikeBackground = /background|backdrop|scene|map|level|bg/i.test(current);
+            var coversCanvas = arguments.length >= 5 && arguments[1] === 0 && arguments[2] === 0 &&
+              arguments[3] >= this.canvas.width * 0.8 && arguments[4] >= this.canvas.height * 0.8;
+            if (looksLikeBackground || coversCanvas) {{
+              this.clearRect(0, 0, this.canvas.width, this.canvas.height);
+            }}
+            return;
+          }}
         }}
         return originalDrawImage.apply(this, arguments);
       }} catch (error) {{