The Official POV-Ray 3.5 syntax for the noise generators was the keyword noise_generator followed by a single integer from 0 to 3. This could be specified either in a pattern or the global settings block.

Slime-POV extends this syntax in order to allow for new features. The Slime-POV noise generator syntax is as follows:

NOISE_GENERATOR:
	noise_generator {
		NOISE_GENERATOR_IDENTIFIER |
		GENERATOR_TYPE
		[slice FLOAT]
		[repeat INTEGER]
		[match_second_derivatives [Bool]]
	}
GENERATOR_TYPE:
	0 | 1 | 2 | 3 | 4

The old syntax is still supported for backward compatability.

Note that you can #declare noise generators just like you can with pigments, textures, functions, etc.

POV-Ray 3.5 allowed 3 types of noise generators: type 1 was implemented in earlier versions of POV-Ray and was somewhat problematic. Type 2 was first implemented in Mega-POV, prior to POV-Ray 3.5, and is the same as type 1, but scaled down to avoid some problems. Type 3 was new in POV-Ray 3.5, and is standard Perlin Noise.

The new type 4 noise generator is similar to type 3, and works the same way internally. The difference is that it is four-dimensional. The value for the fourth dimension can be specified with the slice keyword. This is helpful in animations, where you may want the noise to change smoothly without actually changing its position in 3D space. If you're not going to make use of the 4th dimension, try to avoid using type 4, since it is about twice as slow as type 3, and looks very similar.

A noise generator with type 0 will merely inherit the noise generator specified in global settings, or, if none is specified, type 2 with slice 0, repeat 0, and match_second_derivatives off.

1.2.2.1 Repeating Noise

In Ken Perlin's recent paper, he mentioned a new type of interpolation that matches the second derivatives of the noise function. This significantly reduces a grid artifact when the noise is used as a normal pattern. It is, however, slower to calculate. When necessary, activate it with the match_second_derivatives keyword, which is optionally followed by a boolean switch value. Note that the other improvement that Perlin mentioned in his paper has not been implemented.

Due to the large number of features the noise generator now has, the f_noise3d(x,y,z) function no longer suffices for noise in functions. To make up for this, Slime-POV allows you to declare noise generator functions:

NOISE_GENERATOR_FUNCTION:
	function {
		NOISE_GENERATOR
	}

These are used just like any other function. For instance:

	#declare my_favorite_noise_generator = noise_generator {
		3
		match_second_derivatives on
	}
	#declare my_favorite_noise_function = function {
		noise_generator {
			my_favorite_noise_generator
		}
	}
	sphere {
		0,1
		pigment {
			function {my_favorite_noise_function(x,y,z)}
		}
	}

Type 4 (four dimensional) noise functions take four arguments: one for each dimension (For instance, my_4D_noise_function(x,y,z,w)). The fourth argument overrides the slice parameter.

Anyone who has used a smooth height field to simulate terrain with some flat spots knows about the artifacts that can appear around the flat areas. These artifacts have been removed in Slime-POV.

In addition to the interpolation bugfix, there is also a new type of height field smoothing, that calculates the normals at each point with a different method. The smoothing method can be set with an integer after the smooth keyword as follows:

	smooth 0 | 1 | 2

Zero is no smoothing. One is POV-Ray 3.5's smoothing method. Two is the new smoothing method, which can create more pleasant results. Sometimes the difference is unnoticeable.

All of the "squares" that a height field is made up of are created by two triangles. The division between these triangles, by default, is always diagonally from the upper left of the square to the lower right of the square. By adding the smart_triangulation keyword to a height field, you cause the height field to choose the division line in a way that creates the smoothest result. This causes the height field to take up a little more memory, but the effect is much nicer in some situations.