OBJ材质文件MTL格式分析

OBJ文件不包含面的颜色定义信息，不过可以引用材质库，材质库信息储存在一个后缀是".mtl"的独立文件中。关键字"mtllib"即材质库的意思。 材质库中包含材质的漫射(diffuse)，环境(ambient)，光泽(specular)的RGB(红绿蓝)的定义值，以及反射(specularity)，折射(refraction)，透明度(transparency)等其它特征。  "usemtl"指定了材质之后，以后的面都是使用这一材质，直到遇到下一个"usemtl"来指定新的材质。

Ka r g b

defines the ambient color of the material to be (r,g,b). The default is (0.2,0.2,0.2);

Kd r g b

defines the diffuse color of the material to be (r,g,b). The default is (0.8,0.8,0.8);

Ks r g b

defines the specular color of the material to be (r,g,b). This color shows up in highlights. The default is (1.0,1.0,1.0);

d alpha

defines the transparency of the material to be alpha. The default is 1.0 (not transparent at all) Some formats use Tr instead of d;

Tr alpha

defines the transparency of the material to be alpha. The default is 1.0 (not transparent at all). Some formats use d instead of Tr;

Ns s

defines the shininess of the material to be s. The default is 0.0;

illum n

denotes the illumination model used by the material. illum = 1 indicates a flat material with no specular highlights, so the value of Ks is not used. illum = 2 denotes the presence of specular highlights, and so a specification for Ks is required.

map_Ka filename

names a file containing a texture map, which should just be an ASCII dump of RGB values;