Art

Every solid in this kit is described by one color and a footprint; the three faces are derived. There is no leftColor, because offering one is offering you a way to break the look.

Six rules make procedural art read as designed. They are cheap and they are not optional — a render that skips them still produces a picture, and the picture looks like a placeholder.

silhouette first	a shape you can recognize as a black cutout at thumbnail size. If it needs its detail to be legible, it is the wrong shape
detail at three scales	a mass, a feature on the mass, and something small enough to only just resolve. Two scales reads as a toy
setback massing	stack narrower volumes as they rise. A single extruded box is the shape every naive isometric demo has
window rhythm	repeat with a break — three, three, gap, three. Even spacing reads as a spreadsheet
cool shadows, warm highlights	this is what separates a stylized render from a gray lerp. shade does it for you; do not replace it with a multiply
something moves on everything	every building gets an animate hook. A static frame reads as a screenshot of a game

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The slots, and which of them are fills

createPalette(BASE_SLOTS) names ten colors. It is not a menu of ten interchangeable ones. Two are not fills at all, three do not obey nightfall, and picking one of those for a roof gives you a building that compiles, passes every test, and is wrong at a glance.

slot	day color	it is	use it for
ground	soft green, 58% light	fill	terrain, tiles, earth, anything the world is made of
brand	terracotta, 42%	fill — the recolorable one	whatever the game is about. palette.set('brand', …) is the whole recolor story
metal	blue-gray, 59%	fill	machinery, rails, pipes, hardware
glass	pale cyan, 79%	fill	windows, water, ice, anything wet
sky	pale blue, 77%	fill, backdrop only	clear: 'sky', and the color haze pulls toward
warn ok bad	amber 71%, green 64%, red 39%	signal	lamps, hazards, a legality tint on a ghost, a HUD mark
ink	near-black, 13%	outline and text. Not a fill	the stroke argument of isoTile, isoPatch, isoWall; wallText, sign, screenText; and genuinely black hardware at small area — an iron post, a flue
night	near-black, 8%	not a color you draw with	one place only: the tint argument of light.begin — the color the dark itself goes

palette.ink(value) is the resolver, not the slot. It takes any Ink — a number or any slot name — and returns a color. The name collision with the 'ink' slot is exactly how a roof ends up black.

A fill in the outline slot is a hole in the picture. shade derives three faces from one color, and that spread is what makes a solid legible: brand comes out 42 / 30 / 21% with an outline at 13%. ink comes out 13 / 11 / 9% with an outline at 4% — the whole three-tone read spans four points of brightness, and because the silhouette stroke is derived from the fill there is nothing left below near-black for it to be derived into. It is not a dark building; it is a building with no faces and no silhouette.

A signal in a fill slot does not obey nightfall. warn, ok and bad barely move between DAY and NIGHT — 71→66, 64→58, 39→36 — because a HUD has to stay readable at midnight. ground goes 58→22 and sky 77→14. So a roof painted warn sits at 93% of its noon brightness over a town at 38% of its, and glows all night with nothing anywhere to explain why.

An outline in a fill slot is the milder mirror: stroke with ground or metal and the stroke lands within a few points of the face it is meant to separate, so a crowd of buildings merges into one mass at exactly the zoom where the silhouette was doing all the work.

// A market with two roof materials, picked off the slot list as equals. Half the town renders
// as black holes and the other half glows at midnight.
isoRoof(pen, gx + 0.15, gy + 0.15, w, d, h, 0.72, seed % 2 ? 'warn' : 'ink');

Ten is a starting vocabulary, not a limit. A market with two roof materials wants two slots of its own — added to both stop sets, so both roll at dusk with everything else.

import { DAY, NIGHT, createPalette, extendStops, isoRoof } from '@latticekit/draw';
import type { Pen } from '@latticekit/draw';

const DAY_X = extendStops(DAY, { tile: 0xb4573cff, thatch: 0xc9a15aff });
const NIGHT_X = extendStops(NIGHT, { tile: 0x59323aff, thatch: 0x5f5546ff });
export const palette = createPalette(DAY_X);

export function marketRoof(pen: Pen, gx: number, gy: number, seed: number): void {
  isoRoof(pen, gx + 0.15, gy + 0.15, 1.7, 1.7, 1.4, 0.72, seed % 2 ? 'tile' : 'thatch');
}

---

A sprite

import { VARIANT_ZERO, defineSprite, drawSprite, glowDot, spriteHeightPx } from '@latticekit/draw';
import type { Pen } from '@latticekit/draw';

const LIGHTHOUSE = defineSprite({
  id: 'lighthouse',
  w: 2,
  d: 2,
  // Static art. `rng` is freshly seeded from `v.seed` on every call, so a tower cannot
  // reshuffle itself on reload and a replay from a seed lands on the same pixel.
  massing(s, v, rng) {
    s.shadow(0, 0, 2, 2);
    s.box(0, 0, 2, 2, { color: 'stone', h: 1.2 });                       // the plinth
    s.cylinder(1, 1, 0.72, { color: 'paper', h: 4 + v.level, z: 1.2 });  // the tower
    s.cylinder(1, 1, 0.86, { color: 'stone', h: 0.3, z: 5.2 + v.level }); // the gallery
    s.roof(0.4, 0.4, 1.2, 1.2, 5.5 + v.level, 0.9, 'roof');
    if (rng.next() > 0.5) s.post(0.25, 1.7, 0, 1.4, 'stone');            // a mooring bollard
  },
  // Live art, over the static art, every frame. `pen.t` is the only clock, and it arrived as a
  // parameter — nothing in this package reads one.
  animate(pen, gx, gy, v, _rng, zPx) {
    const sweep = (pen.t * 0.22) % 1;
    const bright = sweep < 0.25 ? 1 : 0.25;
    glowDot(pen, gx + 1, gy + 1, 5.4 + v.level, 'warn', 0.2, snap(bright));
    void zPx;
  },
  // The light it throws into the night. Runs only when the frame has one, and pools it on the
  // ground the tower stands on — `zPx` is the elevation `drawSprite` was given, passed through.
  emit(lights, gx, gy, v, _rng, zPx) {
    lights.add(gx + 1, gy + 1, zPx, 3 * 0.3, 1, 'warn');       // the core
    lights.add(gx + 1, gy + 1, zPx, 3 + v.level, 0.32, 'warn'); // the halo
  },
});

/** Nine levels of brightness. See "an animated color is an allocator", below. */
function snap(x: number): number {
  return Math.round(x * 8) / 8;
}

export function paint(pen: Pen, gx: number, gy: number, groundPx: number): number {
  const v = { ...VARIANT_ZERO, seed: 7, level: 2 };
  drawSprite(pen, LIGHTHOUSE, gx, gy, v, groundPx);
  return groundPx + spriteHeightPx(LIGHTHOUSE, v);   // what DepthSorter.add wants, for culling
}

Three things in there are load-bearing and easy to leave out.

drawSprite's last argument is the ground under the footprint. Leave it off on a heightfield and every sprite floats or sinks by its own terrain height — which reads as the art is wrong, sprite by sprite, rather than as one missing argument. The same number goes to spriteVolume and to DepthSorter.add, and those three agreeing is what stops the picture, the tap target and the sort order disagreeing about which hill this is standing on.

Two add calls, not one, for a light. A single pool is a linear ramp, and the eye reads a linear ramp as the size of the lamp rather than as the reach of its light. Two pools — a small bright core inside a wide dim halo — meet a neighbor in each other's halo, where both curves are nearly flat, instead of in each other's ramp, where the slope is constant and the union has a visible crease down the middle.

spriteHeightPx replays the whole massing to answer. Calling it per sprite per frame is a second full massing pass over the entire scene every frame, for a number that cannot change. Compute it once, when the thing is created.

---

Heights are storeys here and world pixels everywhere else

Every height a sprite author writes — BoxOpts.h, BoxOpts.z, roof's rise, post's h — is in storeys, because "three storeys" is what a person means. Every height that crosses into iso — heightAt, footprintBase, Volume.zPx, DepthSorter.add — is in world pixels. levelsToPx and pxToLevels are the two conversions, and they happen at the boundary.

LEVEL_H is 26, not 32, on purpose: a storey exactly one tile tall makes every building a cube, and cubes read as programmer art.

Pass one unit where the other is expected and the building is 26× wrong, which is at least visible. The dangerous version is subtler: a Volume built in storeys makes boxSilhouette return an outline that is nearly right, so picking works everywhere except near the roof. Use spriteVolume, which does the conversion for you and is the only thing that knows how tall the massing actually built itself.

---

A moving color is a cache key

This one sits two layers below you and no signature states it, so it is worth knowing even though the sharpest version of it has been fixed.

softEllipse — which is what glowDot, contact shadows and every light pool are built on — cannot draw a falloff per call at a sane price, so it renders one small ramp per (inner, outer) color pair and reuses it. The color pair is a cache key.

The key is snapped to 32 levels per channel — the resolution a 64-pixel ramp actually has — and a full cache evicts one entry rather than all of them. So you do not have to quantize colors in your own art code, and if you already did, you can stop. A flame mixed against noise every frame visits at most 32 keys per channel and then hits for ever. (traps has the measured version of what this looked like before the key was snapped: one animated color evicting every other call site's ramp, at 3.74 misses a frame and about 3.7 MB/s of garbage.)

Three things remain true and are what to watch:

• Animating both endpoints along independent paths multiplies pairs rather than adding them — one moving end is 32 keys, two moving independently is 32². Move one end, or move the radius, which is what the eye tracks anyway.
• Your palette counts as an animated color. A day cycle running Palette.lerp on a continuous t every frame moves every slot in the scene at once, so every color in every call becomes a new pair — a whole-scene version of the same failure, with nothing at any call site that looks like an animation. One exhibit found this with 27% of its soft ellipses missing and no flickering light anywhere in it. Palette.lerp quantizes t and bumps rev only when the quantized step moves, which is what absorbs it — so do not defeat that by rebuilding stop sets every frame (see below).
• A two-second color fade steps 32 times rather than 120. Invisible on a soft falloff. If you need a hard edge to move smoothly, Surface.ellipse is exact.

The tell in a profile was never a flicker. It was a game that got slower and stayed slower.

---

Palettes, and the reason a game gets slower at dusk

import { DAY, DUSK, createPalette, extendStops, hexOf, hsl } from '@latticekit/draw';

// HOISTED, at module scope. See below — this is the whole point.
const DAY_X = extendStops(DAY, { sand: 0xe8d9a8ff, foam: 0xf4f8ffff });
const DUSK_X = extendStops(DUSK, { sand: 0xcfa87dff, foam: 0xc9d4e8ff });

const palette = createPalette(DAY_X);
palette.set('brand', hsl(28, 0.62, 0.54));   // one number in the save, never a derived token

export function nightfall(t: number): string {
  palette.lerp(DUSK_X, DAY_X, t);
  return hexOf(palette.get('sky'));
}

lerp compares its stop sets by identity to decide whether the frame changed anything. A set rebuilt inside the render callback bumps rev on every frame — and rev is what every cache in the kit keys on. The symptom is not a wrong color; it is a frame time that climbs at dusk and stays climbed.

Both stop sets must define exactly the same slots. A half-defined night palette is how one thing stays gold at midnight, and the failure is silent everywhere else. extendStops is how you add a color of your own — sand, foam, a faction red — to the transition, rather than redefining the sets.

Store the player's hue, never the #rrggbb it derives to. Derivation needs cbrt and pow, which are not required by the spec to be correctly rounded, so a stored token is an engine-specific artifact in a file that will travel to another engine — and the player gets a world that is a shade off on their phone from what it is on their laptop, with nothing anywhere to explain it.

Palette.lerp quantizes t internally, so a six-second dusk bumps rev 32 times rather than 361. That is deliberate and it is what makes a dusk affordable at all.

---

Terrain, and the axis that is missing

isoTerrain fits a tile whose four corners are at four different heights: it reads the four vertex heights, projects the quad, and shades it by its own cross-slope.

import { isoTerrain } from '@latticekit/draw';
import type { Pen } from '@latticekit/draw';
import type { HeightField } from '@latticekit/iso';

export function paintGround(pen: Pen, field: HeightField, gx: number, gy: number): void {
  //                                                       fill      stroke     tint
  isoTerrain(pen, field, gx, gy, 'ground', undefined, 0.88);
}

Three things about it are load-bearing, and two of them have cost exhibits multiple rebuilds.

The relief is measured east-to-west, because east and west are the two corners that land on the same screen row — the tile's slope along the screen horizontal, which is the only tilt a 2:1 projection can show. That axis is also the sun's: the left face is brighter than the right, so ground rising toward the east corner is the lit ground. Invert the sign and terrain still looks like terrain — terrain lit from the right, under buildings lit from the left, and the picture reads as flat for a reason no screenshot names.

It reads one of the two diagonals, and a landform whose gradient runs along the other one renders perfectly flat. Both corners of a gx + gy slope sit on the same screen row, so the relief term is zero — a six-thousand-foot cliff shading like a texture, with no error and nothing to grep for. If your landform runs that way, supply the north − south term yourself through tint. It is one subtraction and it is the difference between a slope and a cliff.

isoTerrain adds up to ±0.32 of its own relief to whatever tint you hand it. So a flat-ground tint of 1 puts the brightest lit face at 1.5, and shade at 1.5 on a pale rock clips: a fresh mountain sampled at four separate points came back 255, 249, 212 at every one of them, which is not a highlight, it is a hole in the image. Sit the flat-ground tint at about 0.88. And put your own texture in tint rather than in a second shade call — shading twice tints twice, and the ground goes muddy.

---

Three distance bands, and what a cue cannot do

starting carries the shape a first build should take — a world that runs off the edges of the frame, with hundreds of whatever it repeats. Two parts of that are art's.

Depth is three bands: something near, something mid, something far and dimmer. One plane at one scale is why a diorama looks small, and shading will not rescue it, because shading is a function of distance and a picture with one distance in it has nothing to shade. Build the far band out of fewer faces — it is already asked to be dimmer and hazier, which is also permission for it to be simpler, and fidelity at a distance nobody can resolve is the one saving that costs nothing to take.

A cue decorates a structure and cannot replace one. One world shipped every depth cue on this page — haze, three bands of it, cool shadows, warm highlights, a horizon — and still read as a hillside rather than as a mountain, because the composition underneath was wrong: the subject sat entirely inside the frame with air above it. Adding a sixth cue to a scene that is not reading is the move that never works. When something is not reading, check the structure first — what is off the edge of the frame, how much of it is background, how many distance bands there are — and only then reach for another cue.

---

Small things that turn out to be big

One stroke around the silhouette, never one per face. Per-face strokes cross-hatch the interior and destroy the chunky read that makes this style work at thumbnail size. isoBox draws left face, right face, top, then one closed six-point stroke — and that order is a cross-package contract with the hit-tester, not a convention. In a crowd, stroke the shape that is the silhouette or two hundred people become a mesh of hairlines at low zoom.

A wall along the near-far diagonal has zero screen width. World x is (gx − gy) · HALF_W, so a segment whose gx and gy change by the same amount projects to a vertical line and the art is simply not there. isoWall throws and names both tiles; iso.isEdgeOn(ax, ay, bx, by) asks first. An animated endpoint must not be able to sweep through the diagonal.

massing and animate get different Rng streams. A sprite whose massing chose a height and a lean cannot recover either by drawing in the same order in animate, so a moving crown sits beside the static one it is supposed to be and the tree renders with its head beside its neck. Worst on the tallest, leaniest instances, which is why it survives a review. Address by index instead:

import { hashStep, toUnit } from '@latticekit/core';
import type { Variant } from '@latticekit/draw';

/** The same number in `massing` and in `animate`, addressed by position rather than by order. */
export function vat(v: Variant, i: number): number {
  return toUnit(hashStep(v.seed, i));
}

emit gets no clock. Its parameters are (field, gx, gy, v, rng, zPx) — no pen, no t — so a guttering torch or a lamp being switched on cannot be written through the sanctioned hook. Drive it from animate with pen.light?.add(…) instead; two exhibits arrived at that independently.

Haze must not converge on the sky slot. At noon sky is a fully saturated cyan, so mixing a green hillside toward it trades one saturated color for another and the far range stays as loud as the near one. Real distance loses saturation before it loses hue, so the target is the sky pulled a third of the way to white by day and barely at all at night.

Hard color bands on a noisy field make a mosaic of flat diamonds, because adjacent tiles land either side of a boundary. Interpolate the bands over about sixteen quantized stops — which also keeps the ramp cache happy.

---

What this skill does not cover

you want	read
the boot, the loop, the frame	starting
terrain data, roads, paths, walkers	world
picking, ghosts, drag to place	input
a HUD, a panel, a toast	hud
"it's slow" or a frame budget	performance
something that renders and looks wrong	traps

The long-form version of everything here, with the full primitive list, is on disk at node_modules/@latticekit/draw/README.md.