6.3.4 Patterned Textures

From [pov:6.7.5]:
Patterned textures are complex textures made up of multiple textures. The component textures may be plain textures or may be made up of patterned textures. A plain texture has just one pigment, normal and finish statement. Even a pigment with a pigment map is still one pigment and thus considered a plain texture as are normals with normal map statements.

Patterned textures use either a texture_map statement to specify a blend or pattern of textures or they use block textures such as checker with a texture list or a bitmap similar to an image map called a material map specified with a material_map statement.

An example using a texture map is:

  texture {
    gradient x       // this is the PATTERN_TYPE
    texture_map {
      [0.3  pigment{Red} finish{phong 1}]
      [0.3  T_Wood11]    // this is a texture identifier
      [0.6  T_Wood11]
      [0.9  pigment{DMFWood4} finish{Shiny}]
    }
  }

Material Map

Instead of placing a solid color of the image on the shape like an image map, an entire texture is specified based on the index or color of the image at that point. You must specify a list of textures to be used like a texture palette rather than the usual color palette.

MATERIAL_MAP:
    texture
    {
        material_map
        {
            BITMAP_TYPE "bitmap.ext"
            [BITMAP_MODS...] TEXTURE... [TRANSFORMATIONS...]
        }
    }
BITMAP_TYPE:
    gif | tga | iff | ppm | pgm | png | jpeg | tiff | sys
BITMAP_MOD:
    map_type Type | once | interpolate Type

Layered Texture:

A layered texture consists of several textures that are partially transparent and are laid one on top of the other to create a more complex texture. The different texture layers show through the transparent portions to create the appearance of one texture that is a combination of several textures.

You create layered textures by listing two or more textures one right after the other. The last texture listed will be the top layer, the first one listed will be the bottom layer. All textures in a layered texture other than the bottom layer should have some transparency. For example:

  object {
    My_Object
    texture {T1}  // the bottom layer
    texture {T2}  // a semi-transparent layer
    texture {T3}  // the top semi-transparent layer
  }

In this example T2 shows only where T3 is transparent and T1 shows only where T2 and T3 are transparent.