Rendering error for property textures when 'offset/scale' are defined

[javagl]

(This came up while creating specs for #12237 )

The following is a sandcastle that loads an embedded glTF that defines a property texture with a 3-element fixed-length normalized UINT8 array property that defines an offset/scale in its class property:

https://sandcastle.cesium.com/index.html#c=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

It bails out with

An error occurred while rendering.  Rendering has stopped.
DeveloperError: Invalid vec3 value for uniform "u_example_fixed_length_normalized_UINT8_SCALAR_array_offset".
Error
    at new DeveloperError (https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:10062:13)
    at UniformFloatVec3.set (https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:37305:13)
    at ShaderProgram._setUniforms (https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:38269:19)
...

According to the specification, this should be possible.

Some starting points for examining the reason and possible solutions:

• When offset/scale are defined, then u_<name>_offset and u_<name>_scale unforms are inserted in the shader code at

  cesium/packages/engine/Source/Scene/Model/MetadataPipelineStage.js

  Line 650 in 7aefae9

  const { offset, scale } = property;

• The glsl type there is determined to be vec3, even when the type is an array (!), based on

  cesium/packages/engine/Source/Scene/PropertyTextureProperty.js

  Line 247 in 7aefae9

  // fixed-sized arrays of length 2-4 UINT8s are represented as vectors as the

• The offset/scale properties that serve as the values for the unform there are arrays. (They would have to be Cartesian3 for that assignment to work)

While addressing the PR linked above, I've been thrown off a little bit by some "surprising" aspects of the implementation. It is not always apparent what the type of offset/scale should be. One specific aspect that surprised me is that ...

• MetadataClassProperty.offset uses array types (e.g. a 3-element array for a 3D vector)
• PropertyTextureProperty.offset uses object types (e.g. a Cartesian3 for a 3D vector)

Depending on where and how these values are supposed to be used, both can make sense. (Using different types of types in both places maybe not so much...). But in any case, if the "other" type of type is required for a certain task, then this implies some clumsy back-and-forth conversions, and the special handling of "3-element arrays as vec3 in shaders" require additional attention here.

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Edit: When this is fixed, specs that follow the pattern of the one that is now about to be omitted at ed6ad00#diff-e7104646fcc3649a63c2a9e7468b5143778439156f8f4c56fc0e20a8256c4823R3594 may be added.