Rendering

The execution model is in blender-core. Scene lighting and cameras are in blender-lighting-lookdev.

One call

scripts/render_batch.py -- --engine CYCLES --preset final --res 1920 1080 --out //render/hero_#### --frames 1
scripts/render_batch.py -- --preset preview --frames 1-120 --format MP4 --out //render/turntable
scripts/render_batch.py -- --cameras CamA CamB CamC --format EXR_MULTI --out //render/shots/

Presets: preview (Cycles 64 spp, threshold 0.05, 50% res; EEVEE 16), final (512 spp, 0.01; EEVEE 128 + raytracing), product (1024 spp, transparent background). GPU is picked automatically (OptiX > CUDA > HIP > Metal > oneAPI), and the denoiser matches (OptiX or OpenImageDenoise).

Engine choice

Cycles quality levers (ordered by impact)

1. Adaptive sampling (adaptive_threshold 0.01 final / 0.05 preview) + denoise (OIDN with albedo+normal passes, denoising_input_passes="RGB_ALBEDO_NORMAL"). Raising samples alone is the least efficient fix.
2. Light paths: interiors need diffuse bounces ≥ 4. Product shots: total 12, glossy 4, transmission 8–12 for glass. Clamp indirect 5–10 kills fireflies at a small energy cost.
3. Light tree (use_light_tree, on) for many lights. Path guiding (CPU only) for difficult indirect light.
4. Fewer, larger lights beat many small ones. Emissive meshes are noisier than area lights.
5. Persistent data (render.use_persistent_data) speeds up animations and turntables. Use simplify (max subdivision, texture limit) for previews.
6. 5.2: texture cache (render.use_texture_cache, use_auto_generate_texture_cache) cuts memory in texture-heavy scenes by generating .tx mip tiles.

Color management (decide once per project)

• AgX (default): photographic, handles bright highlights. Looks: AgX - Punchy, - Base Contrast...
• Khronos PBR Neutral: shows albedo faithfully. Use it for product/e-commerce and asset reviews, and to match three.js NeutralToneMapping.
• Standard: graphics/UI/texture output that must match pixel values.
• ACES 1.3 / 2.0: VFX pipelines (plates, other DCCs).
• Use exposure (view_settings.exposure), not light power, for global brightness tweaks. Display device sRGB, or Display P3 / Rec.2100 for HDR delivery.

Output formats

• Stills: PNG 8/16-bit (RGBA when the film is transparent) or JPEG for web previews.
• Comp/VFX: EXR multilayer (EXR_MULTI, DWAA 16-bit) with passes (Denoising Data, Cryptomatte, AO, Mist, Z). 5.0 renamed passes: Diffuse Color, Depth, etc.
• Video: render frames first (PNG/EXR), then encode (FFmpeg or the VSE), because a crash mid-MP4 loses everything. Direct MP4 is fine for previews. Set image_settings.media_type before file_format (5.0+).
• Transparent: film_transparent=True + PNG/EXR. A glass-only alpha needs film_transparent_glass.

Compositor (5.0+ API)

ng = bpy.data.node_groups.new("Comp", "CompositorNodeTree"); scene.compositing_node_group = ng
ng.interface.new_socket("Image", in_out="OUTPUT", socket_type="NodeSocketColor")
rl, glare, out = ng.nodes.new("CompositorNodeRLayers"), ng.nodes.new("CompositorNodeGlare"), ng.nodes.new("NodeGroupOutput")
ng.links.new(rl.outputs["Image"], glare.inputs["Image"]); ng.links.new(glare.outputs["Image"], out.inputs[0])

There's no Composite node anymore: the group output is the final image. Many node options are now input sockets (Glare Type, Threshold, Strength), so --describe them with blender-geometry-nodes/scripts/gn_builder.py. File Output node: directory, file_name, file_output_items.

CLI rendering (render farms, CI)

• blender -b scene.blend -E CYCLES -o //out/frame_#### -F PNG -s 1 -e 120 -a renders an animation. -f 10 renders a single frame. Python args go after --.
• -- --cycles-device OPTIX (or CUDA/HIP/METAL/ONEAPI) selects the device without Python.
• Split frames across machines with -s/-e, or with Placeholders + No Overwrite (render.use_placeholder, use_overwrite=False) on shared storage.

Gotchas

• scene.render.engine enum under-reports (add-on engines). Assign in try/except (the script does).
• EEVEE in background still needs a GPU context. In CI without a GPU, use Cycles CPU or Workbench.
• bpy.ops.render.render(write_still=True) writes render.filepath. Without write_still, the result only lives in Render Result.
• Noise in glass/caustics: enable caustics only if needed (caustics_refractive), raise transmission bounces, or fake it with Thin Wall (5.2) for windows.
• Fireflies: clamp indirect, a filter glossy / blur glossy (blur_glossy 0.5–1), and bigger light sources.