Cycles Kernel Extensions

This page documents the C++ kernel-level additions that Industrial CG Platform makes to the Cycles rendering engine.

Deep EXR Kernel Extensions

Pass Types

// intern/cycles/kernel/types.h
PASS_DEEP_COMBINED   // Deep combined RGBA pass
PASS_DEEP_POSITION   // Deep per-sample position data

These pass types are registered in the Cycles film and enable per-sample depth data output in the rendering pipeline.

KernelFilm Fields

// intern/cycles/kernel/types.h (KernelFilm struct)
int pass_deep_combined;     // Film offset for deep combined pass
int pass_deep_position;     // Film offset for deep position pass
int deep_tile_budget;       // Memory budget per tile for deep samples

Deep Output Pipeline

The deep output pipeline extends the standard Cycles film write path:

1. During path tracing, each sample records its depth alongside color data.
2. The film accumulates deep samples per tile, controlled by deep_tile_budget.
3. At output time, deep data is written using the OpenEXR deep image API.

Shadow Color Kernel Extensions

KernelBackground Fields

// intern/cycles/kernel/types.h (KernelBackground struct)
float3 shadow_color;        // World shadow color (RGB)

KernelLight Fields

// intern/cycles/kernel/types.h (KernelLight struct)
float3 shadow_color;        // Per-light shadow color (RGB)

The shadow color is applied in the shadow evaluation path of the integrator, tinting shadow contributions with the specified color.

Lightgroup Lobe Passes

Split Lobe Index System

// intern/cycles/kernel/types.h
int lightgroup_split_index[];   // Per-lightgroup remap from split lobe to film offset

The lightgroup split index is a data array (accessed via kernel_data_fetch) that maps each lightgroup's split lobe pass to its film buffer offset. This replaces the earlier raw device pointer approach.

Film Write Extensions

The following film write functions are extended to support per-lightgroup lobe output:

// intern/cycles/kernel/film/write.h
film_write_lightgroup_split_pass()  // Write to a specific lightgroup lobe pass

Environment Lightgroup Fix

A key correctness fix ensures that world/environment lightgroup lobe passes write correctly even when Background pass and Emission pass are disabled:

// intern/cycles/kernel/integrator/shade_surface.h
// Uses explicit contribution kind instead of pass-offset comparison
// to avoid PASS_UNUSED aliasing when both passes are disabled

Finite Light Lamp-Hit Fix

The ordinary lamp-hit path (PRIMITIVE_LAMP forward hit) now writes into lightgroup lobe passes for finite lights (area, point, spot, sun), while emissive mesh paths remain combined-only:

// intern/cycles/kernel/integrator/shade_light.h
// Finite light forward-hit emission writes into existing lobe family

Environment Fog (Pending)

WARNING

Environment Fog kernel extensions are currently in development and not yet shipped. This section will be populated when the feature is released.

Source Files

File	Purpose
intern/cycles/kernel/types.h	Kernel data structures, pass enums, film fields
intern/cycles/kernel/film/write.h	Film write functions including split lightgroup passes
intern/cycles/kernel/integrator/shade_surface.h	Surface shading with env lightgroup fix
intern/cycles/kernel/integrator/shade_light.h	Light shading with lamp-hit lobe fix
intern/cycles/kernel/integrator/path_trace_tile.h	Tile-level pass readback with split pass identity
intern/cycles/scene/film.cpp	Film setup and pass registration
intern/cycles/scene/light.cpp	Light sync with shadow color
intern/cycles/scene/background.cpp	Background sync with shadow color