VisRTX 26.09

This release is a large overhaul of the RTX device, headlined by a reworked renderer
lineup, sampleable emissive materials (geometry lights), MDL/MaterialX material support,
and a broad set of volume/spatial-field extensions.

⚠️ Breaking changes

• Single, date-based version scheme. VisRTX, the RTX device and the GL device now
  share one YY.MM version driven by the top-level project (26.09), replacing the
  previous per-component semantic versions (the RTX device was last 0.13.0; VisGL
  carried no version at all). There is no patch component: the RTX device's version
  property now reports 260900 (major * 10000 + minor * 100), with version.major =
  26, version.minor = 9 and version.patch always 0. Applications that gate on
  the reported device version need to account for the jump.
• Renderers renamed. directLight → interactive, ambientOcclusion/ao → fast,
  pathTracer/dpt → quality. The default subtype remains and maps to interactive.
• raycast renderer retired. Its functionality is available via the debug renderer's
  new surfaceColor/baseColor modes.
• tonemap renderer parameter renamed to fireflyFilter, and expanded into
  fireflyFilterMode (tonemap, clamp, trim), fireflyFilterSigma,
  fireflyFilterWarmup and fireflyFilterTrim.
• Background no longer participates in light propagation. Background color/image are
  composited in a dedicated pass; only HDRI lights contribute to the light transport. This
  changes images for scenes that previously relied on background bleed.
• analyticalField renamed to customField.
• Minimum ANARI-SDK is now 0.16.0 (was 0.15.0), and aspect follows the ANARI 1.2
  spec behavior.
• Renderer parameter metadata split into per-renderer JSON files, fixing several
  parameters that were missing from device queries.

✨ New features (RTX device)

Emissive materials and geometry lights

• MDL materials with emission are now registered as geometry lights and sampled with
  next-event estimation + MIS, instead of only being visible on direct hits. Covers
  constant, textured, and attribute-driven emission across triangle, sphere, cylinder and
  cone geometry.
• MDL materials publish an emission descriptor built by a device-free static analysis
  pass, with an explicit registration policy (see ADRs 0005–0007).
• Power-proportional light picking in the quality renderer, plus a new
  maxSampledLights parameter on interactive.
• Environment-map (HDRI) MIS with the balance heuristic.

Materials

• VISRTX_MATERIAL_MDL extension is now advertised. mdl materials accept
  sourceType of module, mdle or code (inline MDL source) with a unified
  materialName selector. Material inputs are matched by parameter name, and texture
  inputs accept either a file path (with <input>.colorspace) or an ANARI sampler object.
• New VISRTX_MATERIAL_MATERIALX extension (materialx subtype): MaterialX documents
  are transcoded to MDL at commit time, with support for documentFile/documentInline
  sources, textured inputs spliced as image nodes, standard_surface (including coat and
  textured emission), and runtime resolution of the MaterialX distribution (ADR 0008).
  Requires VISRTX_ENABLE_MATERIALX_SUPPORT=ON (which requires MDL support).
• physicallyBased gained glTF 2.0 KHR extension support, and an opt-in
  physicallyBasedMdl material type is available.

Geometry

• khr_geometry_isosurface support, including linear NanoVDB isosurfaces routed
  through the per-voxel DDA with forward-difference normals.
• New VISRTX_GEOMETRY_SDF extension — SDF surface geometry with blending controls,
  aimed at biological structure visualization.
• Triangle geometry accepts vec3 and vec4 vertex.tangent (with handedness), and
  auto-generates tangents via angle-weighted accumulation when absent.

Spatial fields and volumes

• New extensions: VISRTX_SPATIAL_FIELD_DATA_CENTERING (cell vs node),
  VISRTX_SPATIAL_FIELD_REGION_OF_INTEREST (object-space roi clip box),
  VISRTX_SPATIAL_FIELD_STRUCTURED_RECTILINEAR, and
  VISRTX_SPATIAL_FIELD_NANOVDB_RECTILINEAR.
• Extensible custom/analytic spatial field samplers with texture accessors and lat/lon
  bounds.
• Ratio-tracking transmittance and uniform-sphere NEE for quality volume shadows/
  in-scatter; volume gradient/normal support; rewritten DDA traversal.
• NanoVDB headers updated to 13.0.

Renderer and frame

• New cutPlane (FLOAT32_VEC4) parameter on all renderers.
• New denoiseStart, denoiseMode, aoBlend, fixedAmbientLighting,
  volumeSamplingRateShadows parameters; the denoiser is fed dense per-pixel
  albedo/normal/input estimates and supports tiling for large frames.
• debug renderer gained materialId, surfaceColor, tangent and attribute modes.
• refinementProgress frame property support.

🐛 Fixes and rendering-quality improvements (RTX device)

• Shadow-ray origins lifted onto the smooth surface (Hanika offset); grazing self-shadow
  acne from analytic back-face hits fixed; polygon epsilon offsetting cleaned up.
• MDL emission radiance was π× too bright — corrected.
• Fixed biased uniform-sphere and cosine-hemisphere samplers, pixel-adjacency artifacts in
  AO/hemisphere sampling, and HDRI double-counting between NEE and the miss path.
• PBR shading: diffuse lobe added to the nextRay path, clearcoat lobe sampled, NdotV
  Fresnel diffuse weight, normal-map orientation fixed for glTF models, NaN-safe shading.
• Robust, spec-compliant analytic primitive intersection with correct caps and front/back
  crossing reporting; integer overflow fixed in macrocell index decomposition.
• Correct handling of transmission → alpha in the final frame; matte honours opacity in
  quality; ANARI channel-fill applied to image samplers.
• Several lifetime/memory fixes: SamplerRegistry use-after-free, MaterialRegistry slot
  leak, pipeline/program-group/MDL-module leaks on rebuild, deferred-commit teardown
  ordering, NUL-terminated embedded resources, and internal-object parameter snapshotting
  across buffered re-commits.
• Picking no longer reads a stale ID buffer; face-varying triangle validation null-deref
  fixed.
• Fixed incorrect CUDA texture object updates in image samplers, MDL texture resource
  null/uninitialized access, and MDL texture lookups reading the wrong union member.
• Volume fixes: object scaling in ray marching, infinite accumulation with unitDistance
  of 0, majorant grid computation, side-by-side non-overlapping volumes, NanoVDB sampler
  coordinate-space mapping.

🚀 Performance (RTX device)

• Camera sampling switched to Halton; RNG moved from cuRAND Philox to PCG-XSH-RR-32
  (drops the CUDA::curand dependency).
• Macrocell space-skipping in rayMarchVolume, halved macrocell size, packed opacity
  bounds, strict-bound TF lookups, and decomposition tracking in the Woodcock sampler.
• Adaptive Russian roulette for quality NEE shadow rays, sub-epsilon shadow-trace
  skipping, volume RR depth tuning, and AO trace skipped when the ambient term is invisible.
• MDL texture data kept in its native format on the device with no redundant host or linear
  device copies; textureResults trimmed to 8; sampler table aliased.
• --use_fast_math enabled for OptiX device kernels, double-precision arithmetic trimmed,
  GPU-driven Image2D texel reduction, batched conditional-CDF construction, per-sampler
  volume dispatch via direct callables.
• Volume parameter commits decoupled from BLAS rebuilds; BLAS/volume/light invalidation
  timestamps decoupled.

🔧 Build (RTX device)

• New VISRTX_MIN_ARCH knob declaring the minimum compute capability (default 50 on
  CUDA 12, 75 on CUDA 13; MDL follows it, and VISRTX_ENABLE_NEURAL raises it to 89).
  Requires a GPU of compute capability 5.0+ (7.5+ on CUDA 13).
• New VISRTX_LIBRARY_NAME to build a differently-named ANARI library so a dev build
  can coexist with an official install.
• VISRTX_ENABLE_MATERIALX_SUPPORT is a dependent option on VISRTX_ENABLE_MDL_SUPPORT.
• Externally specified CMAKE_CUDA_ARCHITECTURES is honoured; NVML is optional; optional
  device dependencies respect CMake flags; MDL modules are re-staged on edit rather than
  only at configure time.
• Various Visual Studio/Windows build fixes, glm updated to 1.0, stb_image target
  conflicts with Barney/OWL resolved.

VisGL (GL device)

No functional changes this release — copyright headers were refreshed and contributor
guidance files were added. A prior fix restoring the frontend library link for Windows
builds is included. VisGL now carries the shared 26.09 version.

Documentation

• RTX device README documents the MDL material extension and all four new spatial-field
  extensions.
• New architecture decision records (ADRs 0001–0008) and per-directory CONTEXT.md
  glossaries covering shading via direct callables, pipeline-per-renderer, PTX embedding,
  surface/volume TLAS separation, geometry lights, sampleable MDL emission, the emission
  descriptor registration policy, and runtime MaterialX distribution resolution.