3D Four Seasons

Keep one recognizable place across all four seasons. Each season should change several mutually consistent visual cues while preserving camera state and interactions.

Author the seasonal identity

Inventory deciduous trees, evergreens, exposed surfaces, sheltered surfaces, lights, sky, and existing weather. Use species and climate appropriate to the project; the table is a temperate-scene starting point.

Season	Foliage and ground	Light and atmosphere	Motion
Spring	Fresh foliage; blossom on appropriate species	Soft warm daylight; gentle haze	Sparse petals or young leaves
Summer	Dense deep greens; full ground cover	Stronger daylight; readable shaded greens	Restrained leaf drift and breeze
Fall	Species-specific amber, red, and brown; litter	Lower warm sun; golden haze	More falling leaves
Winter	Bare deciduous branches; retained evergreens; exposed snow	Cool sky fill; pale sun; warm interiors	Optional sparse snow; little leaf drift

Choose particle effects only when they serve the scene. A seasonal selector does not require a storm or a full weather simulator.

Share one state

Use a four-component blend in the order [spring, summer, fall, winter]. Accept autumn as an alias for fall, then normalize to one internal key. The weights start nonnegative and sum to one.

const presets = {
  spring: [1, 0, 0, 0], summer: [0, 1, 0, 0],
  fall: [0, 0, 1, 0], winter: [0, 0, 0, 1],
};
const weights = [0, 1, 0, 0];
let target = presets.summer;
function setSeason(name) {
  const key = name === 'autumn' ? 'fall' : name;
  if (!Object.hasOwn(presets, key)) return false;
  target = presets[key];
  return true;
}
function stepSeason(dt, reducedMotion = false) {
  const a = reducedMotion ? 1 : 1 - Math.exp(-1.4 * Math.min(Math.max(dt, 0), 0.05));
  for (let i = 0; i < 4; i++) weights[i] += (target[i] - weights[i]) * a;
}

Feed the same state into material uniforms, sky, sun/fill lighting, particle density, and optional ambient audio. A new selection should redirect the current blend, not queue another animation or reset to summer. Resolve each result from authored base values and weights; repeatedly tinting last frame's color causes drift.

Change foliage and snow convincingly

Use species-specific color palettes and stable per-instance IDs. Gradually thin deciduous foliage for winter using a deterministic threshold or dither. Preserve evergreen coverage. Apply matching visibility and wind rules to shadow/depth materials so absent leaves do not cast summer shadows.

For inexpensive settled snow, combine winter weight with upward-facing world-space geometric normals and an exposure mask:

snow = winterWeight * smoothstep(0.3, 0.85, worldNormal.y) * exposure

Blend toward a pale, rough snow material. Upward normal alone also whitens sheltered tables and indoor floors; tag exposed objects or supply shelter masks. A material overlay does not add thickness or change silhouette. Add selective snow-cap geometry only for close-up edges where depth matters. Keep falling snow intensity separate from settled coverage if the scene models accumulation and melt.

Keep the transition responsive

Preallocate particle pools and reuse materials/geometry. Change uniforms rather than recompiling shaders or rebuilding the world. Preserve existing material hooks when extending shaders and use stable program cache keys; match the installed renderer's shader chunks instead of assuming an old injection point exists.

Keep season independent of time of day and weather. Derive a final lighting state from those inputs once, so several controllers do not overwrite the same sun or fog values. Refresh expensive environment maps at controlled state changes, with caching where possible.

Use keyboard-accessible controls with a visible selected state and updated accessible labels. Under reduced motion, apply the chosen seasonal appearance immediately and retain a composed still scene. Pause continuous animation while hidden.

Verify

Capture all four seasons from the same camera. Each should be recognizable without its label. Rapidly switch spring → winter → summer → fall mid-transition and check for color drift, stale shadows, allocation spikes, and lost camera controls. Verify snow exposure indoors/outdoors, evergreen retention, particle count, and desktop/mobile rendering.

Read REFERENCES.md. Seijaku demonstrates shared uSeason weights, setSeason, snowInject, foliage thinning, and seasonal light tinting. Full snowfall physics and climate simulation are extensions, not claims about that implementation.