affaan-m/ECC · error · RuntimeError

blender rendered nothing

Error message

blender rendered nothing:
{proc.stdout[-800:]}
{proc.stderr[-800:]}

What it means

render3d.py raises RuntimeError('blender rendered nothing: ...') when the headless blender subprocess finished but produced no turn_*.png frames in the destination directory. The message embeds the last 800 chars of Blender's stdout/stderr to expose the underlying failure.

Solutions

Read the embedded proc.stdout/proc.stderr tail in the message to identify the real Blender error.
Confirm `blender --version` works in the shell and the binary is on PATH.
Fix the root cause in the Blender script — most commonly the mesh file (no mesh in file) or an unwritable dest directory.
Increase the timeout if rendering was killed before any frame was written.

Example fix

// before
render3d.turntable('bad.glb', 'out/')  # blender script raises internally
// after
import trimesh
m = trimesh.load('bad.glb', force='scene')
assert any(g.faces.size for g in m.geometry.values()), 'empty mesh'
frames = render3d.turntable('good.glb', 'out/')

Defensive patterns

Strategy: try-catch

Validate before calling

import shutil
from pathlib import Path
def validate_render_env(mesh_path, dest):
    if shutil.which('blender') is None:
        raise EnvironmentError('blender not on PATH')
    Path(dest).mkdir(parents=True, exist_ok=True)
    if not Path(mesh_path).is_file():
        raise FileNotFoundError(mesh_path)

Type guard

def blender_available() -> bool:
    import shutil
    return shutil.which('blender') is not None

Try / catch

try:
    frames = turntable(mesh_path, dest)
except RuntimeError as e:
    if 'blender rendered nothing' in str(e):
        logger.error('blender failure tail: %s', str(e)[:1600])
        raise  # inspect embedded stdout/stderr for root cause

Prevention

Check `blender --version` before batch renders
Always read the stdout/stderr tail embedded in the message
Ensure dest directory is writable by the blender process
Use a timeout large enough for the frame count and scene complexity

When it happens

Trigger: Calling turntable_blender (or turntable) when the blender binary is missing/fails to launch, the Python script inside Blender throws (e.g. no mesh — see error 922), the output path is unwritable, or the frame render settings produce zero frames before timeout.

Common situations: blender not installed or not on PATH (launch failure surfaces in stderr); the embedded bpy script raised (import error, no mesh); disk permission issues on dest; timeout killing the process mid-render.

Related errors

AI-assisted analysis of affaan-m/ECC@8321021c54 (2026-09-16). Data as JSON: /api/errors/6acead3b0fbb38b9. Report an issue: GitHub.

Appendix: source

Thrown at skills/taste-application/scripts/taste/render3d.py:253

) -> list[Path]:
    dest = Path(dest)
    dest.mkdir(parents=True, exist_ok=True)
    with tempfile.NamedTemporaryFile("w", suffix=".py", delete=False) as fh:
        fh.write(_BLENDER_SCRIPT)
        script = fh.name
    cfg = json.dumps({
        "mesh": str(Path(mesh_path).resolve()),
        "dest": str(dest.resolve()),
        "frames": n_frames, "size": size, "engine": engine,
    })
    proc = subprocess.run(
        ["blender", "-b", "--python", script, "--", cfg],
        capture_output=True, text=True, timeout=timeout,
    )
    Path(script).unlink(missing_ok=True)
    frames = sorted(dest.glob("turn_*.png"))
    if not frames:
        raise RuntimeError(f"blender rendered nothing:\n{proc.stdout[-800:]}\n{proc.stderr[-800:]}")
    return frames


def turntable(
    mesh_path: str | Path,
    dest: str | Path,
    n_frames: int = 48,
    size: int = 768,
    backend: str = "auto",
) -> tuple[list[Path], str]:
    """Render a turntable. Returns ``(frames, backend_used)``."""
    if backend == "auto":
        backend = "blender" if have_blender() else "software"
    if backend == "blender":
        try:
            return turntable_blender(mesh_path, dest, n_frames, size), "blender"
        except Exception:
            # A failed Blender render must not lose the asset; the software

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