Mathematical Expressions

Getting Started

In addition to simple variable reading, there is a more advanced option using mathematical expressions. You can experience the full power of this method using the rpt:expression model.

{
    "model": {
        "type": "rpt:expression",
        "value": "foo + 1",
        "cases": [
            {
                // can specify as a single value:
                "when": [ 6 ],
                // "all" defaults to false. If true, all conditions in "when" 
                // must be met for this case to be selected:
                "all": true 
                "model":  { ... }  // This model will update because 5 + 1 = 6!
            }
        ]
    },
    "rpt": {
        "variables": {
            "numbers": {
                "foo": 5
            }
        }
    }
}

Besides exact matching, in when you can specify other expressions for comparison, constants, and functions. You can find a list of all these in the EvalEx documentation.

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

Game Variables

Along with variables from rpt, game variables can also be used in expressions:

1. Global Variables and Time

Variable	Description	Default Value
gameTime	Total game time in ticks since world creation.	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 refer to the creature (player or mod) holding the item.

Variable	Description	Default Value
holderX	X coordinate of the entity position in the world.	0
holderY	Y coordinate of the entity position in the world.	0
holderZ	Z coordinate of the entity 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 amount of the entity.	20
maxHealth	Maximum possible health of the entity.	20
fallDistance	Entity fall distance.	0
motionX	Speed along the X axis.	0
motionY	Vertical speed (positive when jumping, negative when falling).	0
motionZ	Speed along the Z axis.	0
speed	Total movement speed of the entity.	0
horizontalSpeed	Horizontal movement speed (X and Z).	0
onGround	Whether the entity is on the ground (1 - yes, 0 - no).	0
isSprinting	Whether the entity is sprinting (1 - yes, 0 - no).	0
isCrouching	Whether the entity is crouching (1 - yes, 0 - no).	0
isInWater	Whether the entity is in water (1 - yes, 0 - no).	0
isInLava	Whether the entity is in lava (1 - yes, 0 - no).	0
isSwimming	Whether the entity is swimming (1 - yes, 0 - no).	0
isFallFlying	Whether the entity is flying with elytra (1 - yes, 0 - no).	0
isAlive	Whether the entity is alive (1 - yes, 0 - no).	0
isOnFire	Whether the entity is on fire (1 - yes, 0 - no).	0
isInvisible	Whether the entity is invisible (1 - yes, 0 - no).	0
hurtTime	Time since damage was received (in ticks).	0
deathTime	Time since death (in ticks).	0
invulnerableTime	Remaining invulnerability time (in ticks).	0
age	Entity age in ticks (relevant for passive mobs).	0

3. Player Parameters

Available only if the item is held by a player. Otherwise, standard values are returned.

Variable	Description	Default Value
food	Current player hunger level (0 - 20).	20
saturation	Player saturation level (hidden food scale).	5
experienceLevel	Current experience level (number above experience bar).	0
xpProgress	Progress to next experience level (0.0 to 1.0).	0.0
totalXp	Total player experience amount.	0.0
armor	Total armor points value on the player.	0
air	Current air supply (in ticks).	0
maxAir	Maximum air supply (in ticks).	0
attackCooldown	Current attack readiness (0.0 to 1.0).	0.0
sleeping	Whether the player is sleeping (1 - yes, 0 - no).	0
attackProgress	Animation progress of a hit from 0 to 1.	0
usageProgress	Animation progress of using an item from 0 to 1.	0
isSlim	Is player arms slim: 1 - yes, 0 - no	0

4. Environment and Lightin

Variable	Description	Default Value
lightSky	Sky lighting level at current position (0 - 15).	0
lightBlock	Lighting level from blocks (torches, lamps) (0 - 15).	0
lightTotal	Maximum value between lightSky and lightBlock.	0
biomeTemp	Base temperature of the biome where the entity is located.	0
sunAngle	Solar angle in the sky (0.0 to 1.0).	0.0
moonPhase	Current moon phase (integer from 0 to 7).	0