The constant density function.

The constant density function can be used to create a constant particle distribution that is only constrained by the container object.

The cubic density function.

This is actually a cubic spline.

The polynomial density function for different exponent values.

The exponent is given by the exponent keyword. In case of EXPONENT=0 you'll get a linear falloff.

The following parameters are used to tune the sampling process:

The individual sampling parameters are described in the sections below.

The default number of samples is 10. This is sufficient for simple density fields that don't use turbulence.

High turbulence values and dust halos normally need a large number of samples to avoid aliasing artifacts.

By default jittering is not used. The values should be smaller than 1.0.

Note that jittering is used even if super-sampling is not used.

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Thus the halo color map will be repeated by the specified frequency.

Thus the color entry for density f(r)=0 can be moved to phase\!\!\!\!\mod 1.

Special textures use either a texture_map keyword to specify a blend or pattern of textures or they use a bitmap similar to an image map called a material map (specified with the material_map keyword).

A texture map is specified by...

Where NUM_1, NUM_2, ... are float values between 0.0 and 1.0 inclusive. A TEXTURE_BODY is anything that would normally appear inside a texture {... } statement but the texture keyword and {} braces are not needed. Note that the [] brackets are part of the actual statement. They are not notational symbols denoting optional parts. The brackets surround each entry in the map. There may be from 2 to 256 entries in the map.

For example:

When the gradient x function returns values from 0.0 to 0.3 the red highlighted texture is used. From 0.3 to 0.6 the texture identifier T_Wood11 is used. From 0.6 up to 0.9 a blend of T_Wood11 and a shiny DMFWood4 is used. From 0.9 on up only the shiny wood is used.

Texture maps may be nested to any level of complexity you desire. The textures in a map may have color maps or texture maps or any type of texture you want.

The blended area of a texture map works by fully calculating both contributing textures in their entirety and then linearly interpolating the apparent colors. This means that reflection, refraction and lighting calculations are done twice for every point. This is in contrast to using a pigment map and a normal map in a plain texture, where the pigment is computed, then the normal, then reflection, refraction and lighting are calculated once for that point.

Entire textures may also be used with the block patterns such as checker, hexagon and brick. For example...

Note that in the case of block patterns the texture {... } wrapping is required around the texture information. Also note that this syntax prohibits the use of a layered texture however you can work around this by declaring a texture identifier for the layered texture and referencing the identifier.

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.

When used with mapped file types such as GIF, and some PNG and TGA images, the index of the pixel is used as an index into the list of textures you supply. For unmapped file types such as some PNG and TGA images the 8 bit value of the red component in the range 0-255 is used as an index.

If the index of a pixel is greater than the number of textures in your list then the index is taken modulo N where N is the length of your list of 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:

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

The color of underlying layers is filtered by upper layers but the results do not look exactly like a series of transparent surfaces. If you had a stack of surfaces with the textures applied to each, the light would be filtered twice: once on the way in as the lower layers are illuminated by filtered light and once on the way out. Layered textures do not filter the illumination on the way in. Other parts of the lighting calculations work differently as well. The results look great and allow for fantastic looking textures but they are simply different from multiple surfaces. See stones.inc in the standard include files directory for some magnificent layered textures.

Note layered textures must use the texture {... } wrapped around any pigment, normal or finish statements. Do not use multiple pigment, normal or finish statements without putting them inside the texture statement.

Layered textures may be declared. For example

may be invoked as follows:

If you wish to use a layered texture in a block pattern, such as checker, hexagon, or brick, or in a material map, you must declare it first and then reference it inside a single texture statement. A special texture cannot be used as a layer in a layered texture however you may use layered textures as any of the textures contained within a special texture.