Math Expressions

Getting Started

Beyond simply reading variables, there is a more advanced way to work with them using math expressions. You can experience the full power of this approach with the rpt:expression model:

{
    "model": {
        "type": "rpt:expression",
        "value": "foo + 1",
        "cases": [
            {
                "when": [ 6 ], 
                "model":  { ... }  // This model will be used because 5 + 1 = 6!
            }
        ]
    },
    "rpt": {
        "variables": {
            "numbers": {
                "foo": 5
            }
        }
    }
}

In addition to exact comparisons, you can use other comparison expressions, constants, and functions in when. You can find a full list in the EvalEx documentation.

{
    "model": {
        "type": "rpt:expression",
        "value": "SIN(5) + PI", 
        "cases": [
            {
                "when": [ ">=0" ], 
                "all": true,
                "model": {
                    "type": "model",
                    "model": "item/diamond"
                }
            }
        ]
    }
}

Game Variables

Along with variables from rpt, you can also use game variables in expressions:

1. Global Variables and Time

Variable	Description	Default Value
gameTime	Total game time in ticks since the world was created.	0
dayTime	Time of the current day in ticks (0 to 24000).	0
seed	Unique numeric seed for the current render context.	Passed from context

2. Entity (Holder) Parameters

These parameters relate to the entity (player or mob) holding the item.

Variable	Description	Default Value
holderX	X coordinate of the entity's position in the world.	0
holderY	Y coordinate of the entity's position in the world.	0
holderZ	Z coordinate of the entity's position in the world.	0
yaw	Horizontal rotation of the entity (in degrees).	0
pitch	Vertical rotation of the entity (head tilt).	0
health	Current health of the entity.	20
maxHealth	Maximum possible health of the entity.	20
motionY	Vertical velocity (positive when jumping, negative when falling).	0
age	Age of the entity in ticks (relevant for passive mobs).	0

3. Player Parameters

Only available if the item is held by a player. Otherwise, default values are returned.

Variable	Description	Default Value
food	Current hunger level of the player (0–20).	20
saturation	Saturation level of the player (hidden food scale).	5
experienceLevel	Current experience level (number above the XP bar).	0
armor	Total armor points on the player.	0

4. Environment and Lighting

Variable	Description	Default Value
lightSky	Sky light level at the current position (0–15).	0
lightBlock	Block light level (torches, lamps, etc.) (0–15).	0
lightTotal	Maximum value between lightSky and lightBlock.	0
biomeTemp	Base temperature of the biome the entity is in.	0
sunAngle	Sun angle in the sky (0.0 to 1.0).	0.0
moonPhase	Current moon phase (integer from 0 to 7).	0