2D Lighting (Art Side)

Two paradigms for 2D lighting:

1. Baked into the sprite (classic). Highlights and shadows painted directly. Fast, predictable, locks the lighting direction.
2. Dynamic (engine 2D Lights). Sprite is "neutral" diffuse, engine computes lighting from scene lights at runtime. Allows day/night shifts, point lights, dynamic shadows.

Modern indie pixel art usually combines both: baked rim light + dynamic fill from scene Lights.

Engine systems

Sprite layer separation for dynamic lighting

A "lit-aware" sprite needs (at minimum):

1. Diffuse / albedo: the base color. Drawn flat, no baked shadows.
2. Normal map: surface direction encoded in RGB. (See seamless-textures/SKILL.md for authoring.)
3. (Optional) Emissive / glow mask: pixels that should ignore lighting and stay bright (street lamps, lava, magic). RGB = emission color, alpha = mask.
4. (Optional) Specular / smoothness: where light reflects.
5. (Optional) Self-shadow / occlusion: which surfaces of the sprite shadow other surfaces of the sprite. Rare in pixel art.

Most pixel-art games stop at diffuse + normal + emissive. Adding more is diminishing returns vs hand-painting.

Painting flat diffuse for dynamic lighting

If you'll use 2D Lights, the diffuse should be flat-lit — single ambient lighting condition, no strong shadow side. The engine adds the directional shading.

Typical workflow:

1. Paint with uniform mid-tone shading (no strong light direction).
2. Add ambient occlusion (where surfaces meet — under hat brim, under chin, in joints).
3. Don't paint a strong rim/highlight; engine will do it.

If you instead want classic fully-shaded diffuse, the engine's 2D Light affects it ON TOP of the bake — works but the result is double-shaded (cool effect for dramatic lighting; bad for naturalistic).

Normal map workflow

See seamless-textures/SKILL.md for normal map authoring options (Sprite Lamp, Sprite DLight, Materialize, hand-paint).

For pixel art: normals on small sprites can look strange because neighboring pixels have different normals → light shifts pixel-by-pixel unevenly. Solutions:

• Smooth normals: blur the normal map slightly so light transitions smoothly across small sprites. Loses some surface detail but feels more cohesive.
• Hand-paint flat regions: large flat surfaces of a character (chest, back) should have uniform normal (#8080FF), not noisy.
• Strong normals only at silhouette: where the form turns away from camera, use stronger Z-component variation; flat interior keeps uniform.

Self-shadowing in pixel art

Real-time self-shadow on a pixel sprite is usually not worth it. Dynamic shadows on a 32×32 character look noisy, low-resolution, jittery as the light moves.

Common approaches:

Bake self-shadow into diffuse

The cheap way. Paint the sprite with shadow side darker (lit assumed from upper-left). Limits dynamic lighting (always upper-left feel) but looks sharp.

Use separate top-light and rim-light layers

Author two diffuse variants: top-lit and rim-lit. Engine blends based on light direction. Doubles art cost but feels alive.

Skip self-shadow, rely on directional fill

Flat-painted diffuse + 2D Light gives a soft directional fill. Sprite doesn't really self-shadow, but the rim-light hint feels lit. Works for most indie pixel art.

Emissive / glow

Emissive pixels ignore lighting and stay full-bright. Use cases:

• Street lamps, candles, fireflies, eyes glowing in dark.
• Magic spells, neon signs, lava, screens.
• HUD elements.

Authoring:

• Paint emissive layer in Aseprite (separate layer named "emissive").
• Export as separate texture OR RGBA where alpha = emissive mask.
• Engine shader: final_color = lit_color + emissive_color * emissive_mask.

In Unity URP 2D: assign emissive secondary texture in Sprite Renderer.

Day / night palette swap vs realtime mixing

Palette swap approach

• One palette per time-of-day (day, dusk, night, dawn).
• Engine fades between palettes over X seconds.
• Pros: total artist control, retro look.
• Cons: doesn't react to dynamic lights (torches stay torch-bright at noon and night).

Realtime light mixing

• One neutral / day diffuse.
• Multiple Lights with color tint:
  • Global Light 2D = sun (warm noon, cool night).
  • Point Lights = torches (warm, flicker).
• Pros: dynamic, torches naturally bloom in night, dynamic shadows.
• Cons: can look "modern" vs intended retro feel.

Hybrid (most modern indie)

• Authored ramp shifts per time of day (day uses warm ramp, night uses cool ramp).
• Plus Global Light 2D color tint.
• Plus emissive lights for explicit glow sources.

Stardew Valley uses palette swap (retro fit). Hyper Light Drifter uses realtime. Hollow Knight uses realtime + heavy emissive.

Glow / bloom

Two ways to achieve "glow":

1. Pre-baked glow halo: paint a halo around emissive pixels. No shader needed. Cheaper but static.
2. Post-process bloom: extract bright pixels, blur, add back. Looks dynamic, requires post-process pass (URP volume Bloom override in Unity, post-process shader in Godot).

For pixel art: option 2 conflicts with the pixel-perfect aesthetic (blur softens pixels). Common compromise: enable bloom only on emissive layer, not on the diffuse.

Common bugs

• Double-shaded sprites: fully baked diffuse + dynamic light = shadow stacks. Solution: paint flat diffuse OR flat rim, not both.
• Normal map green channel inverted: light comes from "wrong" direction. Toggle Y-flip in Sprite Renderer / shader.
• Emissive layer also gets lit: forgot to mask out lighting on emissive. Solution: emissive added AFTER lighting, not multiplied.
• Bloom blurs pixels: pixel art aesthetic broken. Limit bloom to emissive mask only.
• Pixel-by-pixel normal noise: sprite looks "wrong" under light. Smooth the normal map.

See also

• seamless-textures/SKILL.md — normal map authoring
• palettes/SKILL.md — palette swap vs realtime
• vfx-2d/SKILL.md — emissive vfx
• Engine: unity-2d-lighting