Radiating graphics: a burst effect around an element, and a radial particle emitter with a lifecycle #379

Context

Two related kinds of emphasis graphic come up in this batch. Both are made of many short strokes radiating from a point, and both take today hundreds of hand-placed nodes generated by a script.

1. burst: a splash of strokes when an element pops

When a pill pops in, a few brush-like strokes radiate from it and vanish. Today it takes N line nodes at computed angles, each with its own draw_in timing.

{ "name": "burst", "delay": 0.2, "duration": 0.4, "count": 8, "length": 40, "gap": 12,
  "width": 4, "color": "#FFB020", "seed": 3, "jitter": 0.2 }

This is an animation effect drawn around the element's box. The strokes draw outward from gap px off the box edge, then retract.

2. A radial emitter with birth, travel, death and respawn

A warp tunnel: hundreds of light streaks shoot from the centre to the edges, accelerating, in a continuous flow, with a dark eye in the middle. particle is deprecated, and the for-each + rand + sin($t) recipe has no lifecycle. The reel 10 study generated 460 nodes in Python, each with its own keyframed trajectory: hundreds of kilobytes of JSON for 3 s.

{ "type": "emitter", "origin": { "x": 960, "y": 540 }, "rate": 180, "life": [0.7, 1.2],
  "direction": "radial", "speed": { "from": 200, "to": 1600, "easing": "ease_in" },
  "spawn_radius": [260, 470], "shape": "streak", "length": [60, 240],
  "color": "#EEF4FF", "seed": 7 }

It is deterministic for a given seed and time, so any frame renders independently, as the parallel renderer requires.

Found in: reel 3 (burst), reel 10 (emitter)