Pass & AOV System

This page documents how Industrial CG Platform extends Blender's render pass and AOV system.

New Pass Types

Deep EXR Passes

Pass Type	Internal Name	Description
PASS_DEEP_COMBINED	Deep Combined	Per-sample RGBA with depth for deep compositing
PASS_DEEP_POSITION	Deep Position	Per-sample world-space position data

Fog Pass (Pending)

Pass Type	Internal Name	Description
PASS_FOG	Fog	Environment fog contribution pass

WARNING

The Fog pass is part of the Environment Fog feature which is not yet shipped.

Lightgroup Lobe Pass Registration

When use_lightgroup_light_pass_aovs is enabled on a ViewLayer, the system registers additional per-lightgroup passes at render setup time.

Registration Flow

Scene sync → Film setup → For each lightgroup:
  → If split passes enabled:
    → Register Combined_<lg>
    → Register Diffuse_Direct_<lg> (if enabled)
    → Register Diffuse_Indirect_<lg> (if enabled)
    → Register Glossy_Direct_<lg> (if enabled)
    → ... (all enabled lobe combinations)

Pass Naming Convention

<Lobe>_<Direction>_<LightgroupName>

Where:

• Lobe: Diffuse, Glossy, Transmission, Volume
• Direction: Direct, Indirect
• LightgroupName: The user-defined lightgroup name

The Combined_<lg> pass is always present for each lightgroup.

Film Offset Mapping

Each registered pass receives a unique offset in the Cycles film buffer. The lightgroup split index array maps:

lightgroup_split_index[lightgroup_id * num_split_types + split_type_index] = film_offset

This is accessed in the kernel via kernel_data_fetch(lightgroup_split_index, index).

Pass Readback

Identity Preservation

A key correctness fix ensures that per-lightgroup split passes are read back through their actual PassType identity, not through the first matching generic pass type. This prevents:

• Direct-only passes appearing empty when indirect-only passes exist.
• Pass content aliasing between different lightgroup lobe combinations.

The fix lives in:

intern/cycles/integrator/path_trace_tile.h

Compositor Integration

Lightgroup lobe passes are exposed as standard Blender render passes and appear in:

• The Blender compositor as Render Layers node outputs.
• The Image Editor's pass selector.
• OpenEXR multilayer output as named layers.

Deep EXR Output Format

When Deep EXR output is enabled:

1. The render pipeline stores per-sample depth data alongside color data.
2. At output time, the OpenEXR deep image API is used to write the deep file.
3. The deep format is compatible with standard deep compositing tools (Nuke DeepRead, etc.).

Deep Tile Budget

The deep_tile_budget parameter controls how many samples per pixel can be stored during tile rendering. Higher values preserve more depth detail but use more memory.

Source Files

File	Purpose
intern/cycles/scene/film.cpp	Pass registration and film setup
intern/cycles/integrator/path_trace_tile.h	Pass readback with identity preservation
intern/cycles/blender/addon/properties.py	Cycles addon pass property definitions
source/blender/render/intern/pipeline.cc	Blender render pipeline pass integration
source/blender/makesrna/intern/rna_scene.cc	RNA pass property definitions
intern/cycles/kernel/types.h	Kernel pass type enumerations