anari-cycles

An ANARI device implementing the Cycles production path tracer from Blender. This lets any ANARI-based application render with Cycles — physically based light transport, the Principled BSDF, motion blur, volumes, denoising, and CPU/GPU (CUDA/OptiX) backends — through the standard, renderer-agnostic ANARI API. The Cycles sources are vendored as a subproject; the device builds as a regular ANARI library (libanari_library_cycles) loadable via ANARI_LIBRARY=cycles.

See BUILDING.md for build instructions (including GPU kernels, denoising, OpenSubdiv, and OpenVDB/NanoVDB options).

Implemented KHR extensions

Beyond the ANARI 1.0 core objects, the device declares the following official KHR extensions (some as trimmed local variants that advertise the official name but omit registry parameters not yet implemented — see device/cycles_device.json):

Camera

• KHR_CAMERA_PERSPECTIVE, KHR_CAMERA_ORTHOGRAPHIC, KHR_CAMERA_OMNIDIRECTIONAL
• KHR_CAMERA_DEPTH_OF_FIELD, KHR_CAMERA_SHUTTER, KHR_CAMERA_ROLLING_SHUTTER
• KHR_CAMERA_STEREO, KHR_CAMERA_MOTION_TRANSFORMATION

Geometry

• KHR_GEOMETRY_TRIANGLE, KHR_GEOMETRY_QUAD, KHR_GEOMETRY_SPHERE
• KHR_GEOMETRY_CYLINDER, KHR_GEOMETRY_CONE, KHR_GEOMETRY_CURVE
• KHR_GEOMETRY_ISOSURFACE
• KHR_GEOMETRY_TRIANGLE_MOTION_DEFORMATION, KHR_GEOMETRY_QUAD_MOTION_DEFORMATION

Instance

• KHR_INSTANCE_TRANSFORM, KHR_INSTANCE_TRANSFORM_ARRAY
• KHR_INSTANCE_MOTION_TRANSFORM, KHR_INSTANCE_MOTION_SCALE_ROTATION_TRANSLATION

Light

• KHR_LIGHT_DIRECTIONAL, KHR_LIGHT_POINT, KHR_LIGHT_SPOT
• KHR_LIGHT_QUAD, KHR_LIGHT_RING, KHR_LIGHT_HDRI
• KHR_AREA_LIGHTS

Material

• KHR_MATERIAL_MATTE, KHR_MATERIAL_PHYSICALLY_BASED

Sampler

• KHR_SAMPLER_IMAGE1D, KHR_SAMPLER_IMAGE2D
• KHR_SAMPLER_PRIMITIVE, KHR_SAMPLER_TRANSFORM

Volume / spatial field

• KHR_VOLUME_TRANSFER_FUNCTION1D
• KHR_SPATIAL_FIELD_STRUCTURED_REGULAR, KHR_SPATIAL_FIELD_STRUCTURED_REGULAR_CUBIC
• KHR_SPATIAL_FIELD_NANOVDB

Renderer

• KHR_RENDERER_AMBIENT_LIGHT, KHR_RENDERER_BACKGROUND_COLOR, KHR_RENDERER_BACKGROUND_IMAGE
• KHR_RENDERER_DENOISE

Frame / device

• KHR_FRAME_ACCUMULATION, KHR_FRAME_COMPLETION_CALLBACK
• KHR_FRAME_CHANNEL_ALBEDO, KHR_FRAME_CHANNEL_NORMAL
• KHR_FRAME_CHANNEL_PRIMITIVE_ID, KHR_FRAME_CHANNEL_INSTANCE_ID, KHR_FRAME_CHANNEL_OBJECT_ID
• KHR_DEVICE_SYNCHRONIZATION, KHR_ARRAY1D_REGION

Notably absent: KHR_SAMPLER_IMAGE3D (Cycles has no dense 3D image textures; creating an image3D sampler warns and yields an invalid object) and KHR_SPATIAL_FIELD_UNSTRUCTURED (no Cycles analogue).

Vendor extensions (CYCLES_*)

These expose Cycles capabilities that have no KHR equivalent, or extend a KHR extension where the standard stops short of what Cycles can do. Introspection definitions live in device/json/cycles_ext_*.json.

Renderer

• CYCLES_RENDERER_SAMPLING_CONTROLS — Fine-grained path-tracing controls on the renderer: per-type bounce limits, direct/indirect sample clamping (firefly suppression), light tree and caustics toggles, glossy filtering, fast-GI approximation, adaptive sampling, film exposure, and pixel filter selection. The ANARI core renderer only defines pixelSamples/ambientColor-level knobs; production tuning of a path tracer needs the rest, and the parameter set is inherently Cycles-specific (defaults match the Cycles socket defaults).

• CYCLES_RENDERER_INTERACTIVE_SCALING — Device-side emulation of the Cycles viewport resolution divider: after a camera/scene change, the first frame renders at reduced resolution (fixed or automatic divider targeting a frame time) and is upscaled, then accumulation restarts at full resolution. Gives ~9–40× faster camera-move frames during interaction. No KHR extension covers progressive-resolution preview rendering.

• CYCLES_RENDERER_DENOISE_START — A denoiseStart renderer parameter (mirroring VisRTX): with denoising enabled, channel.color shows the raw accumulation until the accumulated sample count reaches the threshold, then switches to the denoised result. Extends KHR_RENDERER_DENOISE, which only offers an on/off toggle — early denoised frames can look smeary, and the KHR extension provides no way to delay the denoiser's visible effect.

Lights and light transport

• CYCLES_LIGHT_SKY — A sky light subtype backed by Cycles' Nishita multiple-scattering procedural sky (sun direction/size/intensity, altitude, air/dust/ozone density). It drives the scene background like an HDRI light. Overlaps in spirit with KHR_LIGHT_HDRI, but that extension requires a captured environment image; there is no KHR extension for a parametric physical sky model.

• CYCLES_LIGHT_LINKING — Named light/shadow link sets: a light can be restricted to illuminate (or cast shadows on) only surfaces that opt into its set, following Blender's light-linking semantics. Pure artistic-control feature with no KHR counterpart.

• CYCLES_LIGHTGROUPS — A lightGroup name on lights and surfaces plus per-group frame channels (channel.lightgroup.<name>) that decompose the beauty image into per-group lighting contributions for downstream compositing. No KHR extension defines light AOVs.

Surfaces and geometry

• CYCLES_SURFACE_COMPOSITING — Per-surface ray-visibility flags (camera/diffuse/glossy/transmission/shadow/volume scatter), holdout objects, and shadow catchers whose caught shadows composite into the color channel's alpha. The ANARI core only has a boolean visible; per-ray-type visibility and catcher/holdout workflows are compositing features KHR does not cover.

• CYCLES_GEOMETRY_SUBDIVISION — Catmull-Clark or linear subdivision on triangle/quad geometry with adaptive object-space dicing and edge creases, using Cycles' OpenSubdiv path. KHR geometry extensions describe only fixed, pre-tessellated primitives; render-time subdivision has no KHR equivalent.

Materials and shading

• CYCLES_MATERIAL_SUBSURFACE — Random-walk subsurface scattering parameters (subsurface weight, per-channel radius, scale, IOR, anisotropy) on the physicallyBased material. Extends KHR_MATERIAL_PHYSICALLY_BASED, which defines no subsurface parameters at all.

• CYCLES_MATERIAL_EMISSIVE_STRENGTH — An emissiveStrength scalar multiplier on physicallyBased, mirroring glTF's KHR_materials_emissive_strength. Extends KHR_MATERIAL_PHYSICALLY_BASED, whose emissive is a [0,1] color — the scale factor allows emitted radiance beyond that range.

• CYCLES_MATERIAL_TOON — A toon material subtype exposing Cycles' Toon BSDF (diffuse/glossy component, size, smooth) for non-photorealistic rendering. KHR only defines matte and physicallyBased; a stylized BSDF cannot be expressed through either.

• CYCLES_MATERIAL_HAIR — A hair material subtype exposing Cycles' Principled Hair BSDF (Huang/Chiang models, melanin-based coloring, roughness controls); pairs with KHR_GEOMETRY_CURVE strands. Hair fiber scattering is physically distinct from a surface BSDF and has no KHR material.

• CYCLES_MATERIAL_OSL — An osl material subtype accepting Open Shading Language source (compiled at commit time) or precompiled .oso bytecode, with shader inputs settable as ANARI parameters. Arbitrary programmable shading is far beyond any KHR material. Requires a build with WITH_CYCLES_OSL=ON; otherwise the material warns and is invalid.

Volumes

• CYCLES_VOLUME_PRINCIPLED — A principled volume subtype driving Cycles' Principled Volume node: density from a spatial field, scattering albedo, anisotropy, absorption, emission, and blackbody fire (with an optional temperature field). Overlaps with KHR_VOLUME_TRANSFER_FUNCTION1D in that both render spatial fields, but the KHR volume is a colormapped/scientific-visualization model; this one is a physically based smoke/fire shading model that a transfer function cannot express.

Frame and device

• CYCLES_FRAME_CHANNELS — Additional render passes as frame channels: position, roughness, mist (with renderer mist controls), 2D motion vectors, per-pixel sampleCount, shadowCatcher, and shadowCatcherMatte. Extends the KHR_FRAME_CHANNEL_* family, which stops at albedo/normal/ids — these are the extra AOVs compositors expect from a production renderer.

• CYCLES_DEVICE_SELECTION — Device parameters computeDevice (auto/cpu/cuda/optix/hip/metal/oneapi) and computeDeviceIndex to pick the Cycles compute backend, plus read-only properties listing available backends and reporting the one in use. ANARI has no standard way to select a backend within a device implementation.