Particle Documentation - Curves in Particle Effects

Curves are interpolation values with inputs from 0 to 1, and outputs based on the curve. For each rendering frame of each particle, the curves are evaluated and the result is placed in a Molang variable with the same name as the curve.

Molangvar is the Molang variable to be used in Molang expressions. For example, variable.mycurve in the example below would make the result of the curve available in Molang as variable.mycurve. All variables must begin with variable.

The type can be "linear", "bezier", "bezier_chain", or "catmull_rom".

• linear is a series of nodes, equally spaced between 0 and 1 after applying input/horizontal_range.

• bezier is a 4-node bezier spline, with the first and last point being the values at 0 and 1 and the middle two points forming the slope lines at 0.33 for the first point and 0.66 for the second.

• catmull_rom is a series of curves which pass through all but the last/first node. The first/last nodes are used to form the slope of the second/second-last points respectively. All points are evenly spaced.

• bezier_chain is a chain of bezier splines. A series of points are specified along with their corresponding slopes, and each segment uses its pair of points and slopes to form a bezier spline. Each point aside from the first/last is shared between its pair of spline segments.

nodes are the control nodes for the curve. These are assumed to be equally spaced; this notation only works for linear, bezier, and catmull_rom.

nodes for bezier chain are the control nodes for bezier_chain. The nodes will be sorted prior to parsing, so if you declare nodes 0.3, 0.6, 0.5, they will be re-ordered to 0.3, 0.5, 0.6.

input <float/Molang> This is the input value to use. For example, variable.particle_age/variable.particle_lifetime results in an input from 0 to 1 over the lifetime of the particle, while variable.particle_age would provide input of how old the particle is in seconds.

horizontal range (default: 1.0) This is the range that the input is mapped onto between 0 and this value. This field is deprecated and optional. This field is ignored for bezier_chain

Example

"curves": {
  "Molangvar": {
    "type": type,

    "nodes": [<float/Molang>, <float/Molang>, <float/Molang>, <float/Molang>],

    "nodes": {
        // the key values map to the "input" field
        "0.3": {
            "value": "5", // the output of the curve
            "left_value": "2", // when curve comes from the left of the node, what point does it use?
            "right_value": "3", // when curve comes from the right side of the node, what point does it use?
            "slope": "3", // the slope of the node, both sides
            "left_slope: "0.4", // the left slope of the node
            "right_slope": "2", // the right slope of the node
        },
        ... // more nodes
    },
    "input": <float/Molang>
    "horizontal_range": <float/Molang>
  }
}