ramp

A ramp is a value that changes over 0..1. It is how an effect makes one thing follow another: colour over life, size over speed, opacity over height.

procgen.searchNodes("", { pack = "ramp" }) lists the family and procgen.describeNode("op.<id>") describes any one of them.

Ops

• ramp.keys — a ramp built from keys. Each key is { t = <0..1>, value = ... }, and type says what the value is: a Float, Color ({ r, g, b, a }), Vec2, Vec3 or Vec4 ({ x, y, z, w }). Keys are laid out in t order whatever order they are written in. Between keys the value moves in one of three ways:
  • linear: a straight line from key to key;
  • smooth: eased into and out of each key;
  • constant: each key's value held until the next key.
• ramp.blackbody — the colours a blackbody glows at across a temperature range, as a Color ramp: deep red at the cool end through orange and white to blue at the hot, over from to to kelvin. glow makes the hotter keys brighter; 4 follows the fourth power of temperature that real blackbody radiance does.
• ramp.sample — a ramp read at every element, at the position along it the 0..1 field wired into u names; a value past either end reads that end. The ramp compiles to the element's dispatch, so a solver's particles read it on the device.

field.ramp (g.field.ramp), a node of the field nodebox, reads a ramp at every element by a value it carries: a graph of field.attribute, field.map_range and ramp.sample. By default each element reads it by its own life attribute, so particles change over their lifetime. by names any other attribute, range maps that attribute's values onto 0..1, and wiring t reads the ramp by any field.

A ramp is a graph value like any other. It can be wired, animated (its keys are params) and cached.

Particles coloured by their heat over their life:

local fire = g.op.ramp.blackbody({ from = 900, to = 4000, glow = 1 })
local life = g.op.field.attribute({ name = "life" })
local lit = g.op.attribute.set({ domain = sparks, name = "Cd", value = g.op.ramp.sample({ ramp = fire, u = life }) })