Mod

@addtogroup libnoise @{ @defgroup modules Noise Mods @addtogroup modules @{ Abstract base class for noise modules.

A <i>noise module</i> is an object that calculates and outputs a value given a three-dimensional input value.

Each type of noise module uses a specific method to calculate an output value. Some of these methods include:

- Calculating a value using a coherent-noise function or some other mathematical function. - Mathematically changing the output value from another noise module in various ways. - Combining the output values from two noise modules in various ways.

An application can use the output values from these noise modules in the following ways:

- It can be used as an elevation value for a terrain height map - It can be used as a grayscale (or an RGB-channel) value for a procedural texture - It can be used as a position value for controlling the movement of a simulated lifeform.

A noise module defines a near-infinite 3-dimensional texture. Each position in this "texture" has a specific value.

<b>Combining noise modules</b>

Noise modules can be combined with other noise modules to generate complex output values. A noise module that is used as a source of output values for another noise module is called a <i>source module</i>. Each of these source modules may be connected to other source modules, and so on.

There is no limit to the number of noise modules that can be connected together in this way. However, each connected noise module increases the time required to calculate an output value.

<b>Noise-module categories</b>

The noise module classes that are included in libnoise can be roughly divided into five categories.

<i>Generator Mods</i>

A generator module outputs a value generated by a coherent-noise function or some other mathematical function.

Examples of generator modules include: - noise::module::Const: Outputs a constant value. - noise::module::Perlin: Outputs a value generated by a Perlin-noise function. - noise::module::Voronoi: Outputs a value generated by a Voronoi-cell function.

<i>Modifier Mods</i>

A modifer module mathematically modifies the output value from a source module.

Examples of modifier modules include: - noise::module::Curve: Maps the output value from the source module onto an arbitrary function curve. - noise::module::Invert: Inverts the output value from the source module.

<i>Combiner Mods</i>

A combiner module mathematically combines the output values from two or more source modules together.

Examples of combiner modules include: - noise::module::Add: Adds the two output values from two source modules. - noise::module::Max: Outputs the larger of the two output values from two source modules.

<i>Selector Mods</i>

A selector module uses the output value from a <i>control module</i> to specify how to combine the output values from its source modules.

Examples of selector modules include: - noise::module::Blend: Outputs a value that is linearly interpolated between the output values from two source modules; the interpolation weight is determined by the output value from the control module. - noise::module::Select: Outputs the value selected from one of two source modules chosen by the output value from a control module.

<i>Transformer Mods</i>

A transformer module applies a transformation to the coordinates of the input value before retrieving the output value from the source module. A transformer module does not modify the output value.

Examples of transformer modules include: - RotatePoint: Rotates the coordinates of the input value around the origin before retrieving the output value from the source module. - ScalePoint: Multiplies each coordinate of the input value by a constant value before retrieving the output value from the source module.

<b>Connecting source modules to a noise module</b>

An application connects a source module to a noise module by passing the source module to the SetSourceMod() method.

The application must also pass an <i>index value</i> to SetSourceMod() as well. An index value is a numeric identifier for that source module. Index values are consecutively numbered starting at zero.

To retrieve a reference to a source module, pass its index value to the GetSourceMod() method.

Each noise module requires the attachment of a certain number of source modules before it can output a value. For example, the noise::module::Add module requires two source modules, while the noise::module::Perlin module requires none. Call the GetSourceModCount() method to retrieve the number of source modules required by that module.

For non-selector modules, it usually does not matter which index value an application assigns to a particular source module, but for selector modules, the purpose of a source module is defined by its index value. For example, consider the noise::module::Select noise module, which requires three source modules. The control module is the source module assigned an index value of 2. The control module determines whether the noise module will output the value from the source module assigned an index value of 0 or the output value from the source module assigned an index value of 1.

<b>Generating output values with a noise module</b>

Once an application has connected all required source modules to a noise module, the application can now begin to generate output values with that noise module.

To generate an output value, pass the ( @a x, @a y, @a z ) coordinates of an input value to the GetValue() method.

<b>Using a noise module to generate terrain height maps or textures</b>

One way to generate a terrain height map or a texture is to first allocate a 2-dimensional array of floating-point values. For each array element, pass the array subscripts as @a x and @a y coordinates to the GetValue() method (leaving the @a z coordinate set to zero) and place the resulting output value into the array element.

<b>Creating your own noise modules</b>

Create a class that publicly derives from noise::module::Mod.

In the constructor, call the base class' constructor while passing the return value from GetSourceModCount() to it.

Override the GetSourceModCount() pure virtual method. From this method, return the number of source modules required by your noise module.

Override the GetValue() pure virtual method. For generator modules, calculate and output a value given the coordinates of the input value. For other modules, retrieve the output values from each source module referenced in the protected @a m_pSourceMod array, mathematically combine those values, and return the combined value.

When developing a noise module, you must ensure that your noise module does not modify any source module or control module connected to it; a noise module can only modify the output value from those source modules. You must also ensure that if an application fails to connect all required source modules via the SetSourceMod() method and then attempts to call the GetValue() method, your module will raise an assertion.

It shouldn't be too difficult to create your own noise module. If you still have some problems, take a look at the source code for noise::module::Add, which is a very simple noise module.