Cubiquity for Unity3D  1.2
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Cubiquity.MaterialSet Struct Reference

Represents the combination of materials which a given voxel is composed of. More...

Detailed Description

The use of MaterialSets is one of the more unusual and powerful aspects of the Cubiquity voxel engine, and it is important to understand their use in order to effectivly modify the TerrainVolume through scripts. For simplicity we begin by considering how other voxel engines represent materials and then show how the Cubiquity approach is a logical extension of this.

Most voxel terrain engines (including Cubiquity) are based on the Marching Cubes algorithm, in which the shape of the terrain is defined by an underlying density field. A basic understanding of this algorithm is useful to get maximum benefit from the system, so you may want to consult the link below before going further:

Some voxel terrain engines extend this principle by storing a material identifier (an integer) with each voxel, in addition to the required density value. This material identifier is used at runtime to decide which texture should be applied to different parts of the terrain. However, such a system has a couple of limitations:

  • Transitions between adjacent materials are typically quite sharp and visually unappealing.
  • Level of detail is difficult because such a representation is not easily filterable.

Cubiquity address these shortcomings by adopting a slightly different system. For each voxel we discard both the density and the material identfier, and instead store a set of material weights. These encode the contribution of each material to the voxel, and the density value (required for Marching Cubes) is not stored explicitly but is instead computed on-the-fly as the sum of the these weights.

It is often easiest to work with voxels which are completly full or completly empty, but this is not required and will actually lead to the mesh having a jagged apearance. Partially full voxels can be used to create much smoother surfaces.

A natural question is 'what happens if the sum of the material weights exceeds 255'?. This cannot occur in a traditional voxel engine because the stored density value would be limited by it's 8-bit type, but in Cubiquity it would be possible to set all material weight to '255' and thereby cause the summed value to be significantly greater than this. Basically, you should avoid doing this because it will not behave in an intuitive way.

Practical tips for procedurally generating MaterialSet values

Some of the concepts outlined above may seem confusing, and they do take some getting used to when writing code to procedurally generate volumes. You may find it useful to loosly follow the following process when devising your noise functions for procudural generation.

  1. Start by only using a single material weight, and only set it to either '0' or '255'. Your mesh will have a jagged appearance but at this point you are only interested in defining the general shape of your world.
  2. Move to using full range of values (from 0 to 255) but continue to only use a single material weight. During this stage you are trying to perfect the shape of your world and ensure that you have smooth surfaces where you want them.
  3. Begin working with multiple materials, but only write to a single material for any given voxel. That is, you might decide that a given voxel is 'rock' and it's neighbour is 'snow', but at this point no voxel is a combination of the two. However, the actual value which you write can continue to be thr continuous (0 to 255) value which you derived in the previous step.
  4. (Optional) You may finally decide that some voxel should be composed of multiple materials. From the previous steps you already know what the sum should be, so you just need to decide how to distribute the values to give this sum.

One additional point to keep in mind is that you may find it easier to work with floating point values with a threshold centered at zero, rather than a unsigned byte with a theshold at 127. You are welcome to do this and simply shift/scale/clamp the floating point values just before you write them to the voxel data. This approach may have some performance impact when generating, but it is more intuitive so might be a good starting point at least.

Do note that this is just a suggestion, and you may want to adopt a different workflow. It's worked for us though, and it's generally good to break the process down into such a series of smaller steps.

Public Attributes

ByteArray weights
 The array of weight values controlling the distribution of materials for this voxel. More...
 

Member Data Documentation

ByteArray Cubiquity.MaterialSet.weights

The documentation for this struct was generated from the following file: