Modding ICE


To simplify development and to make its engine reusable, ICE is designed to be as moddable as possible. All entities in the game are loaded from human readable YAML files. Graphics and “scripts” are also loaded from YAML, although different formats might be supported in future.

About the directory structure

ICE has a modular directory system to allow for pluggable mods in future.

Right now, there is only one “mod” - ICE itself. This mod can be found in the data/main and optional user_data/main directories. Any file in data/main can be overridden by a file in user_data/main with the same filename.

Note that user_data/main translates to ~/.ice-game/main after installation on Linux and similar systems.

About bug detection

ICE won’t accept modding data with errors; it’s designed to detect errors and make the modder aware of them. If a mod uses a buggy entity, script, weapon, and so on, ICE will refuse to load it and replace it with an “obviously wrong” placeholder to show that there is a bug. For instance, a buggy entity will be replaced by a violet square with no useful components; a buggy script will be replaced by a script moving the entity up and down repeatedly.

To find more detailed information about what went wrong, look at the ICE log output. On Windows, this is the iceLog.txt file in the directory ICE was launched from. On Linux/POSIX, you can see the log by running ICE from the terminal.

Creating a ship

By convention, ships are stored in the ships subdirectory of a mod directory. For the main game, that is data/main/ships.

Ships are entities - collections of components that specify properties of the ship. For example, a ship might have a visual component - which describes how it is drawn.

To create your own ships, add a new file with contents of the following example in the ships directory.

Alternatively, you can try copying and modifying any ship that already exists there.

Example ship:

visual: visual/player.yaml
  maxSpeed: 300
  acceleration: 2100
    min: [-32, -32]
    max: [32,  0]
  0: weapons/player.yaml
health: 500
  damage: 500
  killsEntity: false

Each item describes a component and its properties. This ship has the following components:

  • A visual component, pointing to the graphics file of the ship.
  • An engine component that can move the ship at most 300 units per second and accelerate at 2100 units per second per second.
  • A volume used for collision detection (for example with projectiles). This volume is an aabbox - axis-aligned-bounding-box, or a rectangle that does not rotate.
  • A weapon component with one weapon at slot 0. There are multiple (256) slots to allow a ship to have more than one weapon.
  • A collidable component that allows the ship to receive collisions. Most projectiles, for example, have a volume but are not collidable - they can’t collide with each other, only with the collidable ships.
  • A health component with 500 maximum health. Entities with a health component die when they run out of health.
  • A warhead component that causes 500 damage and doesn’t kill the ship itself. Warheads are triggered at collision with another entity. This means our ship causes damage to ships it collides with but doesn’t immediately get destroyed. Most projectiles, for example, are destroyed as soon as they collide with something.

There are other components a ship can have. You can see the modding reference pages (linked from ICE documentation index) more detailed information.

Importantly, a ship needs other resources - In this example, a visual component and any weapons it may use. Those are explained below.

Creating graphics (visual component)

Currently the only graphics format supported by ICE is a simple YAML based vector format that stores straight lines with variable colors and line widths.

Graphics are specified by visual components, defined in YAML files in the visual (by convention) subdirectory of a mod directory.

To create your own visual component, you can create a file with the contents of the following example in the visual directory.

You could also try copying and modifying any visual component that already exists there.

Example visual component:

type: lines
  - width: 2
  - color:  rgba40400000
  - vertex: [-7.0, -4.0]
  - color:  rgbA0A0FF
  - vertex: [-1.0, 12.0]

  - vertex: [1.0,  12.0]
  - color:  rgba40400000
  - vertex: [7.0,  -4.0]

  - color:  rgbA0A0FF
  - vertex: [0.0,  8.0]
  - color:  rgba40400000
  - vertex: [0.0,  13.0]

This visual component is a group of lines, currently the only supported visual component type.

Lines are specified by the vertices tag, that allows setting line width, vertex color and vertex itself.

Lines are formed by the 1st and 2nd vertex, the 3rd and 4rd, and so on. The number of vertices must be even.

A color or width entry affects all vertices drawn after it, until the next color or width entry. Default color is white and default width is 1.

Note that width affects only whole lines, while color can change colors of each vertex (which blend in the line, so you can e.g. have a line that blends from a red end to a blue end).

See also:

Visual component

Creating a weapon

Weapons are stored in the weapons (by convention) subdirectory of the mod directory. A weapon fires projectiles (entities) in bursts of one or more projectiles. Each burst takes time to be fired and consumes 1 unit of ammo (which may be finite or infinite). When a weapon runs out of ammo, it can’t fire for a specified reload period.

To create a new weapon, you can create a file with the contents of the following example in the weapons directory.

Alternatively, you can copy and modify any weapon that already exists there.

Example weapon:

burstPeriod: 0.06
ammo: 3
reloadTime: 0.2
 - entity: projectiles/defaultBullet.yaml
   delay: 0.0
       position: [-1.0, 16.0]
       rotation: 0.5deg
       speed:    50.0
       spawnAbsolute: [velocity]
 - entity: projectiles/defaultBullet.yaml
   delay: 0.0
       position: [1.0, 16.0]
       rotation: -0.5deg
       speed:    50.0
       spawnAbsolute: [velocity]
 - entity: projectiles/defaultBullet.yaml
   delay: 0.02
       position: [-2.0, 12.0]
       rotation: 1deg
       speed:    50.0
       spawnAbsolute: [velocity]
 - entity: projectiles/defaultBullet.yaml
   delay: 0.02
       position: [2.0, 12.0]
       rotation: -1deg
       speed:    50.0
       spawnAbsolute: [velocity]

This weapon fires 3 bursts, each taking 0.06 seconds, before reloading for 0.2 seconds. Each burst consists of 4 projectiles shot at different positions (relative to the ship) in different directions (specified in degrees here using the deg suffix). Velocity of the fired (spawned) projectile is absolute, determined by ship’s rotation and firing speed, unaffected by the ship’s own movement.

Two projectiles are fired immediately, the other two 0.02 seconds later. The projectiles are fired at speed 50 and use their engine component (defined in the projectile) to accelerate to full speed.

Each projectile in the burst specifies its own entity file. One burst can consist of projectiles of multiple types. Each projectile is an entity, just like a ship. In fact a weapon could fire ships.

The engine makes no difference between projectiles and ships. When we fire a projectile, we set its position by overriding its physics component. Any component can be overridden by specifying it in components. You can use this, for example, to change projectiles’ visual appeareance or give them specific behaviors by dumbScripts (described below).

See also:

Weapon component

Creating a projectile

Projectiles are found in the projectiles (by convention) subdirectory of the mod directory.

Both projectiles and ships are component based entities. Any component that can be used in a ship can be used in a projectile, and vice versa.

To create a new projectile, create a file with the contents of the following example in the projectiles directory.

Alternatively, you could copy and modify any projectile that already exists there.

Example projectile:

deathTimeout: 1.1
engine :
  maxSpeed       : 2000
  acceleration   : 1000
    min: [-2, -12]
    max: [2,  0]
visual:   visual/defaultbullet.yaml
  damage: 10

Most components of this projectile are the same as ones used in the ship example.

The main differences are:

  • deathTimeout component, which destroys the projectile 1.1 seconds after it’s fired. It is important that projectiles that don’t collide with anything have a limited lifetime so they don’t stay in memory forever.
  • There is no collidable component. This means the projectiles can’t collide with other projectiles - only with collidable ships.
  • The warhead has no killsEntity: false, so the projectile is “killed” after it hits its target.

This projectile has no health or weapons. However, it could have health or weapons, or any other component a ship can have. (For example, a collidable projectile with limited health could be a missile that can be shot down).

Creating a level

Levels are described in YAML files found in the levels (by convention) subdirectory of a mod directory.

To play a level, you must add it to a campaign. This is described in the Creating a campaign section.

A level is composed of definitions of “waves” (groups of enemies spawned simultaneously) and of a level script, which specifies when to spawn a wave.


wave wave1:
    - entity: ships/enemy1.yaml
          position: [360, 32]
    - entity: ships/enemy1.yaml
      delay: 0.1
          position: [440, 64]
          rotation: 0
        dumbScript: dumbscripts/enemy1.yaml

  - effect lines:
      minWidth: 0.3
      maxWidth: 1.0
      minLength: 4.0
      maxLength: 16.0
      verticalScrollingSpeed: 300.0
      linesPerPixel: 0.001
      detailLevel: 7
      color: rgbaC8C8FF30
  - wait: 2.0
  - wave: wave1
  - wait: 2.0
  - wave: [wave1, [50, 150]]
  - wait: 2.0
  - wave:
      wave: wave1
          position: [10, 30]
          rotation: 0.8
  - wait: 5.0

Wave definition

A wave definition starts with a mapping key named wave xxx where xxx is the name of the wave. Wave names must not contain spaces .

There can be any number of wave definitions, but no two waves can have identical names.

A wave is an entity, and a wave definition defines that entity. Waves are generally used to spawn units by setting the spawner component. Spawner is a sequence of entities(units) to be spawned.

Each entity is a mapping with one required key, entity, which specifies filename of the entity to spawn. Optional delay specifies delay to spawn after the wave, in seconds.

Components of an entity can be overridden by components. At least the physics component should be set here to position the entity. The second entity overrides the dumbScript component (explained below), specifying behavior of the spawned unit.

Level script

A level script starts with a mapping key named level, and is composed of instructions and their parameters.

This level is very simple. First, we start a “lines” effect that draws a scrolling starfield background composed of randomly generated lines. After 2 seconds, we spawn a wave. We wait 2 more seconds, and spawn another wave using a different format, changing positions of its entities by [50, 150].

Then we wait another 2 seconds and spawn the a wave again, using the third wave instruction format. Here we make full use of the fact that a wave is actually an entity, and can override any of its components.

Once the script is done, the level ends (the player wins the level). The player loses if their ship gets destroyed before the level is over.

See also:


Creating a campaign

Campaigns are YAML files in the campaigns subdirectory of a mod directory. Unlike other game data, this subdirectory is hardcoded, so the game knows where to look for campaign. A campaign is a simple, sequential list of levels with some metadata. A new campaign can be created by adding another YAML file.


name: ICE demo
  - levels/level1.yaml
  - levels/level2.yaml
  - levels/level3.yaml
  - levels/level4.yaml
  ICE demo campaign:
    - name: Dávid Horváth
    - name: Libor Mališ
    - name: Tomáš Nguyen

This campaign is called ICE demo in game, and it is 4 levels long, specifying filename of each level. It also specifies one credits section, ICE demo campaign, with names of authors of the campaign. This credits section is displayed with game credits when the player clears the campaign.


Creating a DumbScript

Normally when an entity is spawned, it just sits there and doesn’t do anything.

Entity behavior can be controlled by a dumbScript component, which can be set in the entity YAML file or anywhere the entity is spawned (e.g. a wave definition in a level).

DumbScript is a simple YAML based “script” that specifies actions the unit should take. There is no control flow - it just executes instructions one after another. In future, there might be smarter scripts based on a real programming language, e.g. Lua.

DumbScripts are located in the dumbscripts (by convention) subdirectory of a mod directory.

To create a new dumb script, you can create a file with the contents of the following example in the dumbscripts directory.

Alternatively, you could copy and modify any dumb script that already exists there.

Example DumbScript:

- for 0.25:
    move-direction: 0.5
- for 0.5:
    move-direction: -0.5
- for 0.5:
    fire: [0, 1]
- for 0.5:
    move-direction: 0.5
    move-speed: 0.5
    fire: [0]
- for 0.5:
    move-direction: -0.5
    move-speed: 0.5
    fire: [0]
- for 5.0:
    move-direction: 0
- die:

This script moves the entity in a direction of 0.5 radians for 0.25 seconds, then in -0.5 radians for another 0.25 seconds, then it fires weapons 0 and 1 for 0.5 seconds, then moves, at half-speed, in a direction of 0.5 radians while firing weapon 0, and then does the same moving in -0.5 radians. In the end, it moves straight (0 radians) for 5 seconds, and kills the entity.

Note that DumbScripts can be used by any entity. If a dumbScript is in dumbscripts/script.yaml, it will be used by an entity if you add the following code to it:

dumbScript: dumbscripts/script.yaml

Similarly, it can be set in a wave definition in a level. You can even use DumbScripts in projectiles. For example, you could use a DumbScript to create a projectile that moves in a complex fashion and even fires its own weapon.

See also:

DumbScript component