CNA-GAP-036: Runtime glTF import has no unit-scale option; only the offline converters can rescale a model

CNA snapshot 009d40f5  ·  Known Issues › Functional gaps  ·  source links pinned to 009d40f5

ContentManager's glTF reader always imports at unitScale 1.0, so a file not authored in metres must go through the offline converters: cna_tool_gltf_to_cnb --unit-scale, or the optional unitScale argument of cna_tool_gltf_to_cnj.

Identifier

CNA-GAP-036

Category

Functional gap

Subsystem

Models & glTF

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

None

Affected contract

ContentManager::Load<Model> on .gltf/.glb

Expected behaviour

glTF is defined in metres, but many assets are authored in other units; an importer is expected to offer a scale, as CNA's offline tools do.

Actual behaviour at TARGET

The runtime reader in ContentManager.cpp passes 1.0f to every extraction step, and its own comment records the limit: "unitScale is always 1.0 (no CLI-argument equivalent exists for runtime loading); a source file not authored in meters needs the offline tool instead." gltf_to_cnb.cpp accepts --unit-scale <f>; gltf_to_cnj.cpp takes an optional fourth positional argument, unitScale.

Source locations

• modules/content/src/Xna/ContentManager.cpp — ReadGltfModel: 1.0f unitScale arguments and the documented-limitation comment
• tools/gltf_to_cnb/gltf_to_cnb.cpp — --unit-scale option
• tools/gltf_to_cnj/gltf_to_cnj.cpp — --unit-scale option

Evidence

Checked by reading at 009d40f5; not executed.

Independent re-verification: Checked by reading at 009d40f5; not executed. Correction: the original text said both tools accept --unit-scale; only gltf_to_cnb does. Workaround wording: convert with gltf_to_cnb --unit-scale or gltf_to_cnj's positional unitScale, or apply a scale to the world matrix when drawing. Offline scaling is exercised by GltfToCnjToolTests.cpp.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

Scaling is tested through the offline tools; the runtime route has no scale to test.

Regression test

If a runtime option is added (for example on a glTF load-options object), a test that a scaled load matches the tool's scaled output.

Blast radius

Applications that load non-metre glTF files at run time.

Workaround

Convert with --unit-scale, or apply a scale to the world matrix when drawing.