Physics

General

 * No object can exert direct force on any other (except resistance).
 * The player has limited inventory based solely on the number of items.
 * Inventory contents have no physical effect.
 * Mouse clicks must be within an object's visible graphic area to target it.

Object Classes
Each class has distinct game mechanics governing its in-game behaviour.

Tiles

 * Tiles are persistent objects, meaning that they stay in the world where they were last placed regardless of player activity.
 * They can be kept in the player's inventory, placed in the world, and with the exception of townstones, picked up again by their owner.
 * Tiles can only be placed according to a horizontal grid of cells.

Many tiles are 8 pixels high with 16x16 pixel base, and it is sometimes convenient to describe them as "half-tiles", since 16 pixels is conventionally a whole unit in any direction.

Additionally,
 * All tiles can be equipped by selecting them from inventory, making them active.
 * All equippable items are tiles.

There are two basic kinds of tile.

Blocks
Blocks are tiles typically placed in the world as part of permanent constructions. Their appearance conforms to their role as 3d objects, and they are solid where they appear to be.

Equipment
Equipment includes tiles that enhance a character's abilities, and are typically kept with them. If placed in the world, they are transparent but solid half-tiles with their 2d graphic on the top face. Weapons are active equipment, controlled with the spacebar. Zombie heads are equipment, but with some irregular characteristics (see linked article). During use, equipment is displayed on the character with appropriate animations.

Animations, such as Pixel Pistol projectiles and Zombie mouths, are not objects.

Entities

 * Entities exist only while a player is active, and can spawn and despawn according to certain rules.
 * They can not be equipped, kept, or manipulated like tiles.
 * Entities are not bound to grid positions.

There are two basic kinds of entity.

Characters
Player and non-player characters, both benign and hostile. Characters interact physically as solid objects shorter than their apparent size. They are subject to gravity, and will fall if unsupported. Player characters can use equipment with physical effects: Weapons allow them to attack and kill other characters (where allowed). Zombie heads have multiple effects. Accessories are extensions to the character's appearance that can be added and removed freely. They are not kept in inventory, but are accessed via the shop interface.

Accessories are not objects.

Drops
Drops are entities that are displayed in-world for collection only with no other physical attributes. They do not appear as inventory items when collected but have some other effect.

Coins are the only in-game drops. They can be collected using the mouse or by a player character standing on them, which increments the player's gold count.

UPDATE: As of 2013, coins no longer drop from mobs but go directly to your account. This helps against thieves.

Related Topics
Character Physics includes player character attributes and abilities.

Block Properties details physical characteristics and uses of blocks.