World Structure

Game World

The world exists in a three-dimensional coordinate system where the x coordinate runs west to east, the y coordinate runs south to north, and the z coordinate runs bottom to top (in depth). The domain is comprised of a three-dimensional grid of blocks - cubes of unit length - each of which is assigned (at a minimum) a material identifier and a material modifier. As each block is tracked within the engine as an independent entity, additional information can be associated with a block by linking the corresponding component.

Materials

A material defines the base type of a block. The material of a block is specified by a pair of unsigned 32-bit integers, the material ID and the material modifier. The material ID defines the specific type of material (e.g. grass, sand, water). The material modifier indicates which particular appearance of the material the block will take.

Each material specifies three tile sprites: the top face, the side face, and an alternate top face to be shown if a face is obscured. The top face is the horizontal surface in the xy plane, and the side face is the vertical surface in the xz plane.

Blocks

The world is constructed of a collection of blocks as described above. A block is a unit cube (in position units) with side lengths equal to the tile dimension (in pixels) when rendered. Material blocks must be of unit length, but other entities may have arbitrary dimensions. All entities (material blocks and otherwise) are positioned by the lower-bottom-left corner of the unit length block whose base is centered on the bottom plane of the entity. This choice of coordinates allows us to specify the three-dimensional range of a block as starting with its position coordinate \((x, y, z)\) and ending at \((x+1, y+1, z+1)\).

The game world is composed of a non-overlapping set of blocks positioned at integer coordinates on a three-dimensional grid. By non-overlapping, we mean that each coordinate (x,y,z) (where x, y, and z are signed integers) is the position of zero or one blocks. The absence of a block at a coordinate implies that the special “air” block exists at that position. The “air” block is not stored in memory as a real block; it is only used to imply the absence of a block which enables certain optimizations when transferring world data from server to client.

World Segments

The game world is normally handled in small three-dimensional regions known as world segments. Each world segment is a cube having a length of 32 blocks, therefore containing up to 32768 blocks per world segment. The game state is loaded, unloaded, and synchronized one world segment at a time.