Specification

The renderer implements a documented static glTF 2.0 GLB subset. This section brings supported features, known limits and verification evidence together. It is not a claim of complete glTF conformance or Khronos certification.

Supported features and limits

Resource loading is self-contained: one GLB binary buffer, embedded PNG/JPEG images or image data URIs, with no network fetching.

Feature	Status
GLB 2.0 container, indexed and non-indexed triangles, strips and fans	Supported
Node hierarchy, matrix/TRS transforms, negative scale	Supported for static geometry
Sparse and strided vector/index accessors, normalized integer attributes	Supported for consumed mesh attributes
Missing normals	Flat per-face normals; provided tangents ignored
Metallic-roughness material, normal/AO/emissive maps, vertex colour	Supported; classic and studio lighting are approximations
Colour conventions	Linear material/vertex factors, sRGB colour textures, linear lighting and alpha; explicit legacy base-factor option
Alpha modes	Opaque, mask and depth-ordered blend; finite transparent-layer budget
Samplers	Wrapping, nearest/bilinear and all glTF mip filter combinations
Texture coordinates	UV0 and UV1; higher referenced sets fail
KHR_texture_transform, KHR_materials_unlit, KHR_materials_emissive_strength	Supported
KHR_lights_punctual	Directional, point and spot; inverse-square/range/cone attenuation
Authored cameras and scene selection	Supported; camera instances selected by node index
Animation, skins, morph targets	Not rendered; structured diagnostics, or errors in strict mode
Points and lines	Skipped with diagnostics, or errors in strict mode
External resources, additional buffers, compressed geometry/textures	Unsupported; required extensions fail
Transmission, volume, clearcoat and other material extensions	Unsupported; optional extensions use core fallback with diagnostics
Shadows	First directional light only; opaque/masked casters; no point/spot or transparent-caster shadows
HDR environment maps, anisotropic filtering, bloom	Unsupported

Diagnostics include a stable code, JSON-pointer-style path, and human-readable message. Diagnostics cover the entire asset, including unused scenes. Strict mode rejects any reported unsupported feature. The loader validates consumed data and important structural constraints, but is not a replacement for a full asset validator.

Coverage and verification

The detailed checklist is generated from the inventory checked by CI.

What the counts mean

• Implemented + tested: implementation and a named regression test for the scoped behavior.
• Partial support: implementation exists, with a documented limit such as UV0/UV1 only or a finite transparent-layer budget.
• Unsupported: the rendering feature is absent. Testing its warning or strict-mode error does not count as rendering support.
• Needs targeted tests: implementation exists, but a dedicated correctness assertion is missing.

The detailed checklist links every entry to the relevant specification, implementation, targeted tests and reference assets. Entries differ in scope, so their counts are not a conformance percentage or code-coverage measurement.

Three kinds of evidence

Targeted regression tests check specific results: colour-channel arithmetic, camera clipping, transformed normals, alpha compositing, accessor bounds and other individual behaviors. Native Rust tests and Node tests against the built WebAssembly package cover different parts of the implementation.

Khronos reference assets exercise real asset layouts offline. The suite validates each fixture before and after repacking it into GLB, then checks visible output, repeatable rendering and expected diagnostics from two views. These smoke tests do not compare pixels with an independent reference renderer. Embedded fixture resources are repacked for the test; they do not imply runtime support for external resources.

Inventory checks verify fixture hashes, named test declarations, implementation paths and generated documentation. CI runs these after the executable tests. An inventory check alone does not establish that the tests passed.

Run the checks

npm run build
npm test
cargo test
npm run spec:check

After updating test/spec-coverage.json, run npm run spec:report to regenerate the detailed checklist and machine-readable inventory. Reference asset hashes and source provenance live in test/reference-assets.json.

Detailed checklist

Tracked glTF static rendering behaviors, not an exhaustive normative-clause inventory or certification.

This checklist tracks 41 behaviors: 31 implemented, 5 partial, 5 unsupported, 0 unverified. These counts are not a percentage of the glTF specification, code coverage, or Khronos certification. Rows vary in scope and are not weighted.

Implemented means the named behavior has implementation and targeted regression evidence. Partial means known limits remain. Unsupported means rendering is absent, even when its diagnostic is tested. Unverified means code exists but targeted correctness evidence is missing. None implies exhaustive testing of every valid input.

The offline reference suite contains 16 assets, pinned to Khronos glTF Sample Assets revision 8f492390ddc7. Source and vendored hashes are recorded in test/reference-assets.json; attribution is in test/fixtures/NOTICE.md. External resources are embedded in text fixtures, then buffers are repacked into one GLB for tests. This does not exercise external resource loading.

Every reference is validated before and after repacking with glTF Validator, then rendered from two views with nonempty-output, deterministic-output and expected-diagnostic assertions. These are smoke tests, not reference-image comparisons. Validator results concern asset validity, not renderer conformance.

Run npm run build, npm test, and cargo test for executable evidence. Run npm run spec:check to verify checklist references, pinned fixture hashes and generated documentation; it does not execute the tests. CI runs all four. npm run spec:report updates this page and writes build/spec-coverage.json, which records inventory counts without claiming a test run passed.

ID	Tracked behavior and specification	Status
GLB-01	Chunk framing, ordering and unknown trailing chunks	implemented
ASSET-01	Major/minor version and minimum version negotiation	implemented
RESOURCE-01	Buffer resource loading	partial
SCENE-01	Scene selection, hierarchy and application extras	implemented
TRANSFORM-01	Right-handed rotation	implemented
TRANSFORM-02	Inverse-transpose normal transforms	implemented
TRANSFORM-03	Mirrored transforms with tangent handedness	implemented
ACCESSOR-01	Strided normalized mesh attributes	implemented
ACCESSOR-02	Sparse accessors and zero-initialized bases	implemented
ACCESSOR-03	Sparse index precision, ordering and bounds	implemented
ACCESSOR-04	General accessor shapes and consumers	partial
GEOMETRY-01	Triangle strip and fan winding, degenerates	implemented
GEOMETRY-02	Non-indexed triangles	implemented
GEOMETRY-03	Flat normals when normals are absent	implemented
GEOMETRY-04	MikkTSpace tangent generation and UV selection	implemented
GEOMETRY-05	Points and lines	unsupported
MATERIAL-01	Linear factors and sRGB base colour textures	implemented
MATERIAL-02	Metallic B and roughness G channels multiply factors	implemented
MATERIAL-03	PBR appearance and energy response	partial
MATERIAL-04	Occlusion affects indirect light only	implemented
MATERIAL-05	Emissive factor and sRGB texture	implemented
MATERIAL-06	Back-face culling and double-sided visibility	implemented
ALPHA-01	Factor, vertex and texture alpha for OPAQUE/MASK/BLEND	implemented
ALPHA-02	Linear depth-ordered blending	partial
TEXTURE-01	PNG embedded and data URI image loading	implemented
TEXTURE-02	JPEG image decoding	implemented
TEXTURE-03	Texture coordinate sets	partial
TEXTURE-04	Nearest, linear and mip filter combinations	implemented
TEXTURE-05	Wrapping at positive and negative UV boundaries	implemented
TEXTURE-06	Linear-light mip generation and non-power-of-two sizes	implemented
CAMERA-01	Perspective and orthographic node cameras, aspect and clipping	implemented
DEFORM-01	Animation evaluation	unsupported
DEFORM-02	Skin deformation	unsupported
DEFORM-03	Morph target evaluation	unsupported
EXTENSION-01	Required extension rejection and optional extension diagnostics	implemented
EXTENSION-02	KHR_texture_transform	implemented
EXTENSION-03	KHR_materials_unlit	implemented
EXTENSION-04	KHR_materials_emissive_strength	implemented
EXTENSION-05	KHR_lights_punctual	implemented
EXTENSION-06	Spot cone attenuation and light addition	implemented
EXTENSION-07	Other extensions, including compressed geometry and advanced materials	unsupported

GLB-01

Chunk framing, ordering and unknown trailing chunks: implemented. Specification.

Implementation: src/core/gltf/mod.rs.

Targeted regression evidence:

• GLB ignores unknown trailing chunks and rejects invalid chunk layout

ASSET-01

Major/minor version and minimum version negotiation: implemented. Specification.

Implementation: src/core/gltf/mod.rs.

Targeted regression evidence:

• asset versions honor minor forward compatibility and minimum requirements

RESOURCE-01

Buffer resource loading: partial. Specification.

Implementation: src/core/gltf/mod.rs.

Reference smoke tests: BoxInterleaved.

Limitations: One embedded GLB buffer only. External and data URI buffers and multiple buffers are unsupported; reference tests repack buffers before loading.

SCENE-01

Scene selection, hierarchy and application extras: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs.

Targeted regression evidence:

• scene selection, metadata, node indices and parent translations are independent of extras

TRANSFORM-01

Right-handed rotation: implemented. Specification.

Implementation: src/core/math.rs.

Targeted regression evidence:

• y_rotation_is_right_handed

TRANSFORM-02

Inverse-transpose normal transforms: implemented. Specification.

Implementation: src/core/math.rs.

Targeted regression evidence:

• normal_matrix_inverts_scale

Reference smoke tests: NegativeScaleTest.

TRANSFORM-03

Mirrored transforms with tangent handedness: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/material.rs.

Targeted regression evidence:

• normal maps use authored or MikkTSpace tangents, strength, and mirrored node transforms

Reference smoke tests: NegativeScaleTest.

ACCESSOR-01

Strided normalized mesh attributes: implemented. Specification.

Implementation: src/core/gltf/accessor.rs.

Targeted regression evidence:

• interleaved_normalized_colors_keep_their_stride_and_default_alpha

Reference smoke tests: BoxInterleaved, BoxVertexColors.

ACCESSOR-02

Sparse accessors and zero-initialized bases: implemented. Specification.

Implementation: src/core/gltf/accessor.rs.

Targeted regression evidence:

• sparse_zero_base_normalized_colors_and_strided_overrides

Reference smoke tests: SimpleSparseAccessor.

ACCESSOR-03

Sparse index precision, ordering and bounds: implemented. Specification.

Implementation: src/core/gltf/accessor.rs.

Targeted regression evidence:

• sparse_indices_preserve_u32_precision_and_validate_order_and_bounds

ACCESSOR-04

General accessor shapes and consumers: partial. Specification.

Implementation: src/core/gltf/accessor.rs.

Limitations: Coverage focuses on consumed mesh vectors and indices; padded MAT2/MAT3 and animation/skin consumers are not implemented.

GEOMETRY-01

Triangle strip and fan winding, degenerates: implemented. Specification.

Implementation: src/core/gltf/mod.rs.

Targeted regression evidence:

• triangle strips and fans preserve winding and skip degenerate triangles

Reference smoke tests: MeshPrimitiveModes.

GEOMETRY-02

Non-indexed triangles: implemented. Specification.

Implementation: src/core/gltf/mod.rs.

Targeted regression evidence:

• non-indexed triangles match indexed geometry

Reference smoke tests: TriangleWithoutIndices.

GEOMETRY-03

Flat normals when normals are absent: implemented. Specification.

Implementation: src/core/gltf/mod.rs.

Targeted regression evidence:

• missing normals render hard edges and ignore supplied tangents

GEOMETRY-04

MikkTSpace tangent generation and UV selection: implemented. Specification.

Implementation: src/core/gltf/tangents.rs.

Targeted regression evidence:

• normal maps generate tangents from their selected UV set and handle degenerate UVs

GEOMETRY-05

Points and lines: unsupported. Specification.

Implementation: src/core/gltf/scene.rs.

Targeted regression evidence:

• unsupported content has structured diagnostics and a strict load policy

Reference smoke tests: MeshPrimitiveModes.

Limitations: Skipped with diagnostics; strict loading rejects them.

MATERIAL-01

Linear factors and sRGB base colour textures: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/material.rs.

Targeted regression evidence:

• linear colour factors are the default, with an explicit legacy load option

Reference smoke tests: BoxTextured.

MATERIAL-02

Metallic B and roughness G channels multiply factors: implemented. Specification.

Implementation: src/core/material.rs.

Targeted regression evidence:

• metallic and roughness maps use linear B and G channels and multiply factors in both lighting modes

MATERIAL-03

PBR appearance and energy response: partial. Specification.

Implementation: src/core/lighting.rs.

Targeted regression evidence:

• studio metal reflects the environment and roughness changes direct highlights

Limitations: Classic and studio are approximate lighting models; no calibrated Khronos Sample Viewer image comparisons or complete energy-conservation audit.

MATERIAL-04

Occlusion affects indirect light only: implemented. Specification.

Implementation: src/core/material.rs.

Targeted regression evidence:

• occlusion affects indirect lighting only, with strength, and does not dim emission

MATERIAL-05

Emissive factor and sRGB texture: implemented. Specification.

Implementation: src/core/material.rs.

Targeted regression evidence:

• emissive textures decode sRGB, ignore texture alpha, and require an emissive factor

MATERIAL-06

Back-face culling and double-sided visibility: implemented. Specification.

Implementation: src/core/geometry.rs.

Targeted regression evidence:

• a_back_face_is_culled_unless_double_sided

ALPHA-01

Factor, vertex and texture alpha for OPAQUE/MASK/BLEND: implemented. Specification.

Implementation: src/core/material.rs.

Targeted regression evidence:

• texture, vertex and factor alpha multiply only for BLEND and MASK

ALPHA-02

Linear depth-ordered blending: partial. Specification.

Implementation: src/core/transparency.rs, src/core/framebuffer.rs.

Targeted regression evidence:

• BLEND composites in linear depth order and survives PNG round-trip

Limitations: Bounded depth peeling limits overlapping transparent layers; transparent materials receive but do not cast shadows.

TEXTURE-01

PNG embedded and data URI image loading: implemented. Specification.

Implementation: src/core/gltf/images.rs.

Targeted regression evidence:

• one image can be shared by colour and data slots without sRGB contamination

Reference smoke tests: BoxTextured.

TEXTURE-02

JPEG image decoding: implemented. Specification.

Implementation: src/core/gltf/images.rs.

Targeted regression evidence:

• jpeg_textures_decode_to_linear_colour_with_opaque_alpha

TEXTURE-03

Texture coordinate sets: partial. Specification.

Implementation: src/core/gltf/mod.rs, src/core/texture.rs.

Targeted regression evidence:

• texture transforms select UV1, compose scale then rotation then offset, and work when required

Reference smoke tests: MultiUVTest.

Limitations: UV0 and UV1 only; higher referenced sets are rejected.

TEXTURE-04

Nearest, linear and mip filter combinations: implemented. Specification.

Implementation: src/core/texture.rs.

Targeted regression evidence:

• sampler_filters_select_and_interpolate_levels_and_texels

TEXTURE-05

Wrapping at positive and negative UV boundaries: implemented. Specification.

Implementation: src/core/texture.rs.

Targeted regression evidence:

• wrapping_handles_signed_boundaries_in_both_axes

TEXTURE-06

Linear-light mip generation and non-power-of-two sizes: implemented. Specification.

Implementation: src/core/texture.rs.

Targeted regression evidence:

• odd_sized_mipmaps_preserve_the_full_image_average

CAMERA-01

Perspective and orthographic node cameras, aspect and clipping: implemented. Specification.

Implementation: src/core/gltf/scene.rs, src/core/camera.rs.

Targeted regression evidence:

• authored cameras honor node transforms, clip planes, and aspect ratio

Reference smoke tests: Cameras.

DEFORM-01

Animation evaluation: unsupported. Specification.

Implementation: src/core/gltf/scene.rs.

Targeted regression evidence:

• unsupported content has structured diagnostics and a strict load policy

Reference smoke tests: AnimatedTriangle.

Limitations: Static node state only; animation is diagnosed, or rejected in strict mode.

DEFORM-02

Skin deformation: unsupported. Specification.

Implementation: src/core/gltf/scene.rs.

Targeted regression evidence:

• unsupported content has structured diagnostics and a strict load policy

Reference smoke tests: SimpleSkin.

Limitations: Skinning is not evaluated; rest geometry is rendered with a diagnostic, or rejected in strict mode.

DEFORM-03

Morph target evaluation: unsupported. Specification.

Implementation: src/core/gltf/scene.rs.

Targeted regression evidence:

• unsupported content has structured diagnostics and a strict load policy

Reference smoke tests: AnimatedMorphCube.

Limitations: Morph targets and weights are not applied; diagnosed, or rejected in strict mode.

EXTENSION-01

Required extension rejection and optional extension diagnostics: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs.

Targeted regression evidence:

• a required extension is rejected by name

EXTENSION-02

KHR_texture_transform: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs, src/core/material.rs.

Targeted regression evidence:

• texture transforms select UV1, compose scale then rotation then offset, and work when required

Reference smoke tests: TextureTransformTest.

EXTENSION-03

KHR_materials_unlit: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs, src/core/material.rs.

Targeted regression evidence:

• required unlit ignores lighting and emission but preserves culling and alpha

Reference smoke tests: UnlitTest.

EXTENSION-04

KHR_materials_emissive_strength: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs, src/core/material.rs.

Targeted regression evidence:

• emissive strength retains HDR energy until exposure and tone mapping

Reference smoke tests: EmissiveStrengthTest.

EXTENSION-05

KHR_lights_punctual: implemented. Specification.

Implementation: src/core/gltf/mod.rs, src/core/gltf/scene.rs, src/core/material.rs.

Targeted regression evidence:

• punctual lights use authored units, inverse-square falloff, range, colour and transforms

Reference smoke tests: PointLightIntensityTest.

EXTENSION-06

Spot cone attenuation and light addition: implemented. Specification.

Implementation: src/core/punctual.rs.

Targeted regression evidence:

• spot cones fade smoothly and multiple lights add independently

EXTENSION-07

Other extensions, including compressed geometry and advanced materials: unsupported. Specification.

Implementation: src/core/gltf/scene.rs.

Targeted regression evidence:

• unsupported content has structured diagnostics and a strict load policy

Limitations: Only the four named extensions above are supported. Required unknown extensions fail; optional ones use available core fallback with diagnostics.