Another data-specific compression technique is recognizing that certain numbers fall within a well-defined range and re-coding them using a reduced number of bits per value, or re-coding floats as fixed point.

You could also use lossy compression, although there's an obvious trade-off between improving bandwidth and perceptual degradation of the spooled content.

But compression on the actual scene geometry can only be taken so far. To further increase the spooling scene complexity, we need to look at procedural content.

Procedural Content

Procedural content is content that's generated from a mathematical description of the underlying form of that content, and a set of parameters that describe the specific instance of that content.

All forms of content can be expressed in procedural form to one extent or another. For example, music can be stored in MIDI format.

Speech can be stored as annotated text and converted using a text-to-speech converter. Textures can be generated with algorithmic patterns and combined archetypal layers. Animations can be generated based on archetypes and physical constraints.

The most relevant form of procedural content in the context of spooling is procedural geometry. As the player moves through a spooling world, the majority of new content that needs to be spooled is usually the environment geometry and the geometry of any new entity models.

Environment geometry can be divided into two types: natural and artificial. Natural geometry consists of things found in nature, such as natural terrain and rock formations, trees, flowers, vegetation, rocks, rivers, streams, lakes, smoke, and clouds. Artificial environment geometry is anything man-made (or alien-made, if that's your game), like roads, buildings, telegraph poles, walls, light poles, steps, ladders, and fences.

There are some obvious differences between natural and artificial environment geometry. Artificial geometry tends to have a lot of straight edges, flat surfaces, right angles, and identical components, like bricks.

Natural geometry has more curved edges, curved surfaces, and components that are similar but not the same, such as leaves and branches.

Figure 1: A procedurally generated tree of 65,000 polygons is generated from just 48 bytes.

The irregular nature of natural environment geometry results in a large number of polygons used to accurately represent the variety found in real life. Figure 1 shows the archetypical form of procedurally generated natural content: a tree.

Trees and plants are formed based on fairly simply mathematical procedures, and the shape of a tree consisting of thousands of polygons can be represented in less than a hundred bytes.

Natural geometry is hence the most obvious candidate for compression using procedurally generated geometry.