COLLADA - Materials missing not None in Scene

[EtaLoop]

If some materials are omitted, there are not set to None in Scene. Instead there are Some with default values.
I don't know if that's the behavior wanted. If that the case, it would be nice to see that in the documentation ;-)

Example :

let cube = r##"<?xml version="1.0" encoding="utf-8"?>
    <COLLADA xmlns="http://www.collada.org/2005/11/COLLADASchema" version="1.4.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <asset>
        <contributor>
        <author>Blender User</author>
        <authoring_tool>Blender 2.79.0 commit date:2018-03-22, commit time:14:10, hash:f4dc9f9d68b</authoring_tool>
        </contributor>
        <created>2018-11-19T22:54:36</created>
        <modified>2018-11-19T22:54:36</modified>
        <unit name="meter" meter="1"/>
        <up_axis>Z_UP</up_axis>
    </asset>
    <library_images/>
    <library_effects>
        <effect id="Material-effect">
        <profile_COMMON>
            <technique sid="common">
            <phong>
                <specular>
                <color sid="specular">0.5 0.5 0.5 1</color>
                </specular>
            </phong>
            </technique>
        </profile_COMMON>
        </effect>
    </library_effects>
    <library_materials>
        <material id="Material-material" name="Material">
            <instance_effect url="#Material-effect"/>
        </material>
    </library_materials>
    <library_geometries>
        <geometry id="Cube_001-mesh" name="Cube.001">
        <mesh>
            <source id="Cube_001-mesh-positions">
            <float_array id="Cube_001-mesh-positions-array" count="24">-0.5 -0.5 -0.5 -0.5 -0.5 0.5 -0.5 0.5 -0.5 -0.5 0.5 0.5 0.5 -0.5 -0.5 0.5 -0.5 0.5 0.5 0.5 -0.5 0.5 0.5 0.5</float_array>
            <technique_common>
                <accessor source="#Cube_001-mesh-positions-array" count="8" stride="3">
                <param name="X" type="float"/>
                <param name="Y" type="float"/>
                <param name="Z" type="float"/>
                </accessor>
            </technique_common>
            </source>
            <source id="Cube_001-mesh-normals">
            <float_array id="Cube_001-mesh-normals-array" count="18">-1 0 0 0 1 0 1 0 0 0 -1 0 0 0 -1 0 0 1</float_array>
            <technique_common>
                <accessor source="#Cube_001-mesh-normals-array" count="6" stride="3">
                <param name="X" type="float"/>
                <param name="Y" type="float"/>
                <param name="Z" type="float"/>
                </accessor>
            </technique_common>
            </source>
            <vertices id="Cube_001-mesh-vertices">
            <input semantic="POSITION" source="#Cube_001-mesh-positions"/>
            </vertices>
            <triangles material="Material-material" count="12">
            <input semantic="VERTEX" source="#Cube_001-mesh-vertices" offset="0"/>
            <input semantic="NORMAL" source="#Cube_001-mesh-normals" offset="1"/>
            <p>1 0 2 0 0 0 3 1 6 1 2 1 7 2 4 2 6 2 5 3 0 3 4 3 6 4 0 4 2 4 3 5 5 5 7 5 1 0 3 0 2 0 3 1 7 1 6 1 7 2 5 2 4 2 5 3 1 3 0 3 6 4 4 4 0 4 3 5 1 5 5 5</p>
            </triangles>
        </mesh>
        </geometry>
    </library_geometries>
    <library_controllers/>
    <library_visual_scenes>
        <visual_scene id="Scene" name="Scene">
        <node id="Cube" name="Cube" type="NODE">
            <matrix sid="transform">1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1</matrix>
            <instance_geometry url="#Cube_001-mesh" name="Cube">
            <bind_material>
                <technique_common>
                <instance_material symbol="Material-material" target="#Material-material"/>
                </technique_common>
            </bind_material>
            </instance_geometry>
        </node>
        </visual_scene>
    </library_visual_scenes>
    <scene>
        <instance_visual_scene url="#Scene"/>
    </scene>
    </COLLADA>
    "##;

    let scene = mesh_loader::collada::from_str(&cube);

    if let Ok(scene) = scene {
        println!("mat : {:?}", scene.materials);
        assert_eq!(scene.materials[0].color.emissive, None);
        assert_eq!(scene.materials[0].color.ambient, None);
        assert_eq!(scene.materials[0].index_of_refraction, None);
        assert_eq!(scene.materials[0].color.diffuse, None);
        assert_eq!(scene.materials[0].shininess, None);
    }

[taiki-e]

The relevant code is here, and IIRC the behavior here is mostly refers that of assimp. (However, some of it is specified in the spec.)

mesh-loader/src/collada/effect.rs

Lines 439 to 450 in 44ad136

	emission: ColorAndTexture::new([0.0, 0.0, 0.0, 1.0]),
	ambient: ColorAndTexture::new([0.1, 0.1, 0.1, 1.0]),
	diffuse: ColorAndTexture::new([0.6, 0.6, 0.6, 1.0]),
	specular: ColorAndTexture::new([0.4, 0.4, 0.4, 1.0]),
	// refs: https://www.khronos.org/files/collada_spec_1_5.pdf#page=250
	transparent: ColorAndTexture::new([1.0, 1.0, 1.0, 1.0]),
	reflective: ColorAndTexture::new([0.0, 0.0, 0.0, 1.0]),
	shininess: 10.0,
	index_of_refraction: 1.0,
	reflectivity: 0.0,
	// refs: https://www.khronos.org/files/collada_spec_1_5.pdf#page=250
	transparency: 1.0,

We refer to the behavior of assimp because this library was started to replace the use of assimp in our other projects, and it was more convenient to have the same behavior. And the STL parser has a similar behavior.

mesh-loader/src/stl/mod.rs

Lines 147 to 148 in 44ad136

	// Use the same default color (light gray) as assimp: https://github.com/assimp/assimp/blob/v5.3.1/code/AssetLib/STL/STLLoader.cpp#L183-L184
	let mut default_color = [0.6, 0.6, 0.6, 0.6];

That said, the OBJ parser, which was added later than these two parsers, does not have this behavior (defaults to None), and in fact, it may make sense to all parsers do the same as the OBJ parser (aside from the default value specified in the spec).

mesh-loader/src/obj/mod.rs

Lines 1189 to 1205 in 44ad136

	// Colors
	ambient: Option<[f32; 3]>,
	diffuse: Option<[f32; 3]>,
	specular: Option<[f32; 3]>,
	emissive: Option<[f32; 3]>,
	alpha: Option<f32>,
	shininess: Option<f32>,
	illumination_model: Option<u8>,
	index_of_refraction: Option<f32>,
	transparent: Option<[f32; 3]>,
	roughness: Option<f32>,
	metallic: Option<f32>,
	sheen: Option<[f32; 3]>,
	clearcoat_thickness: Option<f32>,
	clearcoat_roughness: Option<f32>,
	anisotropy: Option<f32>,

[EtaLoop]

Ok I understand 👍