pixelfx

pixelfx

Pixel art effects as code. Each effect is one file, src/fx/<category>/<name>.js, that draws into two buffers: color (pixels: opaque, dithered or truly translucent) and light (additive glow). No images, so an effect can be played live, recolored, mirrored, reseeded and rendered to a sprite sheet for any engine.

The method is Hugo Duprez's (How to make (good) pixel art effects with Claude): code is clay, trust your eyes, feed your references. One-shot prompts make mediocre effects. Drafts you render, look at and refine make good ones.

Before anything

1. Work in a pixelfx checkout. If the working directory has no tools/render.mjs, clone one next to the project: git clone https://github.com/patch-gg/pixelfx. No install step: the tools use only Node.
2. Check it runs: node tools/render.mjs fire/torch writes records/fire/torch/contact.png. Open that PNG with your image-reading tool. That contact sheet is how you see every effect from now on.

1. Look for an existing effect first

node tools/list.mjs <words> searches ids, names, tags and descriptions (node tools/list.mjs frost, node tools/list.mjs slash loop). docs/CATALOG.md lists everything by category. Render the candidates and look at them before choosing. Most requests are an existing effect with different options:

• palette: the main ramp, dark to bright, as hex strings. Any PAL ramp in src/core/color.js (fire ember lava smoke dust ice water electric volt poison holy heal arcane shadow blood earth stone gold leaf wood metal bone neon cyber matrix candy night) or your own. A blue fire is {"palette": PAL.ice}.
• seed for a different but equivalent take; flip to face left; angle to rotate; light (0..1+) for glow strength; plus each effect's own knobs in its meta.options (size, count, radius, text, height...).
• Try options without editing code: node tools/render.mjs fire/torch --opts '{"palette":["#102","#215","#43a","#8cf","#fff"]}'.

2. Put it in the game

Canvas or WebGL games in JS or TS (plain canvas, Phaser, PixiJS, Kaplay, three.js): use the code directly. It has no dependencies; copy src/core and the effect files you need, or depend on the repo.

import { createFrame, clearFrame, createFx, composite } from "pixelfx";   // src/core/index.js
import * as frostNova from "pixelfx/fx/ice/frost-nova";                   // src/fx/ice/frost-nova.js

const frame = createFrame(320, 180);            // the game's pixel resolution; ox, oy scroll it with the camera
const img = new ImageData(320, 180);
const fx = createFx(frostNova, { x: hero.x, y: hero.y, flip: hero.facing < 0 });

// every tick
fx.update(dt);
clearFrame(frame);
fx.draw(frame, "back");    // what goes behind characters
drawCharacters();          // your own sprites, or draw them into frame.color yourself
fx.draw(frame, "front");
composite(frame, img.data, background);   // color over the background plus light; or null for transparent
ctx.putImageData(img, 0, 0);              // then scale the canvas up with image-rendering: pixelated
if (fx.done()) removeIt();               // one-shots end on their own; fx.stop() fades a loop out

Several effects can share one frame. In a WebGL engine, upload the composited RGBA to a texture each frame, or render the effect to a sprite sheet once (below) and play it like any other animation.

Any engine (Godot, Unity, GameMaker, Defold, LÖVE, Bevy, Construct): export sprite sheets. node tools/render.mjs ice/frost-nova --sheet writes records/ice/frost-nova/frost-nova.png (transparent frames in a grid) and frost-nova.json (Aseprite-style frames, so Phaser's atlas loader, Godot and Unity Aseprite importers and most tools read it; meta.pixelfx has fps, loop, frame size, columns and the pivot). Set the pivot to meta.pixelfx.pivot (the effect's origin, e.g. the feet), import with nearest-neighbour filtering and no compression, and play at meta.pixelfx.fps. Glow is baked into the sheet as color with alpha, which reads as additive over dark scenes; for bright scenes, render a recolored version or keep the effect on a dark layer.

For the full library: node tools/render.mjs <category> --sheet does a whole category.

A hit needs a body behind it. An effect alone looks like a sticker. Effects with a character carry an act: when the body winds up, when to freeze, how the target reacts. Use it whichever way the game is built:

• With the stock character: createAct(slash, { x, y }) instead of createFx. act.update(dt), act.draw(frame), and throw the picture by act.shake. It holds still by itself during a freeze. node tools/act.mjs <id> --sheet bakes the lot into a sprite sheet.
• With the game's own character: read the timing, slash.act or meta.pixelfx.act in a sheet's JSON (windup, recovery, hits with t and freeze). Play the character's attack animation windup seconds before the effect, and at each hit stop updating everything, effect and characters both, for freeze seconds. Host-side hit-stop works on any effect, with or without an act.

src/fx/moves/ has whole attacks chained from the effects, wind-up to recovery: start there when someone asks for a move, not an effect.

3. Make a new one

Read docs/AUTHORING.md first: it is the contract (meta, draw(p, t, o) for pure effects or create(o) for simulated ones, local coordinates, seamless loops, ending empty), the toolkit, the painter API and the quality bar. Then:

1. Say it in one line with art direction: what it is, how it moves, its palette, its timing. "A frost nova: crystals erupt in a ring from the feet outward, a white flash at the center, shards spin off, the floor stays frosted and fades."
2. Find references in the library: node tools/list.mjs <words>, then read the two or three closest effect files and borrow their techniques (Particles and Bits in src/core/sim.js for sparks, smoke and debris, p.disc for translucent volumes, cycle for seamless particles, tileFbm scrolls for flames and water). Look at the closest of Hugo Duprez's effects too: they are the quality bar. If his has more detail, light or life at the same size on screen, yours isn't done.
3. Draft. node tools/new.mjs <category>/<name> (add --loop for a loop) gives a working file. When the direction is open, write 3 to 5 genuinely different drafts (<name>-a.js .. -e.js), render them all (node tools/render.mjs "<category>/<name>-*") and look at every contact sheet before choosing. Show the user the strongest two or three if they're around (--gif makes animations to share).
4. Look, judge, fix. Render, open records/<id>/contact.png, and judge like a picky pixel artist. Fix the worst thing, render again. Three rounds minimum; a showpiece takes more. --all shows every frame, --mp4 shows motion at full speed.
5. Act it out if a character is involved: add export const act (see "Acts" in docs/AUTHORING.md), with a wind-up before t = 0, a pose change on the release frame, a freeze on contact and a recovery. node tools/act.mjs <id> shows consecutive 12 fps steps: judge motion from those and from --mp4, not from a contact sheet's samples.
6. Check. node tools/check.mjs <id> catches drawing outside the canvas, one-shots that don't end empty, loop seams, unseeded randomness and slow frames, and in an act: keys out of order, unknown pose fields and hands that teleport. Fix until it passes clean. Delete the drafts you didn't keep.

What to look for, and the usual fix:

you see	fix
it reads as mush at 1x	fewer colors, a clear silhouette, one focal point, bigger shapes
speckle: lone noise pixels inside shapes	threshold noise less, quantize with at(), no noise on small shapes
floaty, no punch	fast in, slow out (ease.outQuart/outExpo), a 1 to 2 frame white hero frame, shorter total time
stiff or mechanical	vary every particle (size, speed, delay, life), add secondary motion (sparks, smoke, debris)
washed out	less glow (k 0.2 to 0.5), darker edge steps, keep white for the hottest core only
flat	light from one side: brighter top-left, darker bottom-right step; a darker ramp step at the base
smooth gradients, vector look	hard ramp steps in color; softness only in light and in translucent smoke
a checkerboard where smoke should be	SMOKE, VAPOUR or DUST particles, or p.disc: truly translucent, lit on top
seam when a loop wraps	cycle, loopNoise(phase), whole-cell tileNoise scrolls, sin(phase * TAU * n)
a one-shot that pops off	let it shrink, dither out or fall away before t = duration
a great effect on a dead character	give it an act: wind-up, release pose, freeze on contact, a target that reacts, recovery
the act feels weightless	a wind-up the opposite way to the blow, a longer freeze (up to 0.2 s), a bigger silhouette change, shake
the hit lands out of sync	move the hit key to the effect's own constant, not to a time you eyeballed
he holds the weapon badly	keep a bend in the elbow, shafts in front of the chest; on a swing the blade lags the hand; arms reach about 15 px and don't stretch, so step the body in
his arms cross or the pose looks flat	he faces three-quarters towards us: for open arms the near hand goes left (fx < 0), far hand right, with turn: 1; yaw really turns him

Directional effects face right, ground effects stand on y = 0, actor effects wrap o.actor (a 24 x 38 stock character's mask and pixels), and nothing uses Math.random. Generic motifs are fine; never recreate a specific game's sprites, characters or logos.

4. Native code instead of JS

If the game can't run JS and a sprite sheet isn't enough (an effect that follows a moving target, or needs per-instance colors at runtime), port the effect. Pure effects are a function of time; simulated ones step the particles in src/core/sim.js. Keep the two-buffer idea, the 4x4 Bayer threshold for dithered alpha and the palette ramp lookups. Render the JS original and your port side by side to check they match.