Materials

Materials are nothing more than a glorified set of parameters to the rendering software (shader). In theory, the rendering system is simply:

render(mesh, material)

where the mesh specifies the geometry, and the material everything else.

In practice, there are a number of different rendering systems and even more model formats that store materials, and as such, the Material class must cater to all of them. Dent tries to take a “catch-em-all” approach, where each material has as many parameters as it can, and it is up to the renderer to discard that are not useful.

Parameters of a Material

If you are writing a shader for the default Dent material system, you can expec to be fed a number of textures and constants. They are as listed at the bottom of this document, with details. In brief, though, they are:

parameter	uniform name	type	description
diffuse color tint	diffuse_tint	vec3	a constant by which to multiply the colormap
metallic tint	metallic_tint	float	a constant by which to multiply the metallic map
roughness tint	specular_tint	float	a constant by which to multiply the roughness map
color texture	colormap	sampler2d	the fragment diffuse/albedo value
normal texture	normalmap	sampler2d	the fragment normal map
specularity texture	specularmap	sampler2d	the fragment specularity value
metallic texture	metallicmap	sampler2d	the fragment metallic value
roughness texture	roughnessmap	sampler2d	the fragment roughness value

As you can see, this covers most of the required inputs to Blinn-Phong or Cook-Torrance BDRFs, and so can be used with the builtin lighting shaders.

Parsing Materials from Models

Importing materials is a pain for two reasons. The first is that, unlike meshes, there’s no consensus on what information should be stored with an object with regard to its materials. The second is the way that pyassimp deals with this problem: it doesn’t.

As a result, under the hood, Dent has to do some fancy footwork to guess the right parameters for the material. This unfortunately may require some work from the artist/developer. The exact specifics of the defaults chosen are detailed below.

Parameters

All texture maps described below can be overridden (see Overriding Textures).

Diffuse and Albedo

Most shaders require some sort of colour data. For Phong shaders, this is the diffuse colour. For PBR it is known as the albedo.

In Dent this data is passed as the diffuse colour tint and the colour texture. The correct way to compute the actual value is to multiply the two together.

The default for the image is a blank white texture. The default for the colour is the assimp default of all black. The tint can be specified in any way that is parsed to the COLOR_DIFFUSE property of assimp, and the map in any way that can be parsed to the first texture in the diffuse stack. As an example, in OBJ material format:

newmtl my_material
Kd 0.640000 0.640000 0.640000
map_Kd color.tga

Normal Maps

Normal maps are also stored as part of materials. They are only stored as textures.

The default texture is a single (0,0,1) valued (r,g,b) texture. Any map passed to the first layer of the normal stack of assimp is valid, as is any map passed to the first layer of the bump map. As an example in OBJ material format:

newmtl my_material
map_Bump normal.tga.

Phong Specific Parameters

The specularity is a measure of the coefficient of specularity in Blinn-Phong lighting. It is stored as a texture only. Any map passed to the first layer of the specular stack of assimp is valid. As an example in OBJ material format:

newmtl my_material
map_Ks specular.tga

PBR Specific Parameters

The parameters of roughness and metallic are specific to PBR shading. They are stored in the roughness texture and tint, and the metallic texture and tint parameters. Again, the correct value is obtained by multiplying the two.

Currenly the only way to set these textures is to override them. The tints default to 1.

Overriding Textures

Any of the above textures can be overridden, by placing appropriate image files in the same directory as the model. The format for the image filename is {material_name}.{suffix}.png, where the {suffix} is given from the below table

Texture type	Suffix
Diffuse	diff
Normal	norm
Specular	spec
Roughness	roug
Metallic	meta

Debugging Materials

You can use the Dent asset inspector to view materials and their properties, once they have been loaded into an asset datastore. This is useful to study the values for the tints and textures that are actually parsed by Dent. To do this, run dent-assets inspect, and navigate to the material in question and hit enter to examine its properties.

API