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name: gamedev-2d-art-seamless-textures description: | Seamless / tileable textures for 2D: offset-and-paint trick, mirror techniques, repetition reduction (variant tiles + decoration overlays), transitional tiles (corner / edge / T-junction), normal map authoring for 2D lighting (Sprite Lamp / Sprite DLight / Materialize), procedural base + hand-pixel overlay, roof/floor/wall specializations.

USE WHEN: painting tilesets that don't visibly seam, fixing repetition, adding normal maps to 2D for dynamic lighting, mixing procedural and hand-painted texture. allowed-tools: Read, Grep, Glob

Seamless / Tileable Textures

A "seamless" texture wraps without visible seam at the edges. Critical for any tile that fills regions (grass, dirt, stone, water).

The offset-and-paint trick

Standard workflow to make any texture seamless:

1. Open your texture (e.g., 32×32 px) in Aseprite/PS/Krita.
2. Filter → Offset/Wrap by (16, 16) — the seam now runs through center.
3. Paint over the visible seam with clone-stamp / hand pixel.
4. (Optional) Offset back by (-16, -16) to verify no new seam.
5. Place 2×2 copies of your tile in a test area and inspect.

In Aseprite: Edit → Shift → Wrap (or simply Filters → Offset in v1.3+). Krita: Filter → Other → Offset. Photoshop: Filter → Other → Offset.

Mirror techniques

Quick seamless without offset paint: mirror horizontally + vertically. Always seamless because edges are mirrored to themselves.

Trade-off: visible mirror symmetry at the seam line. Fine for organic materials (rocks, dirt) viewed at small scale, terrible for anything recognizable (bricks would mirror to fake structure).

Repetition reduction

A single seamless tile placed 100 times is visibly repetitive, even if seamless. Solutions:

Variant tiles

Paint 3-5 variants of the "interior" tile. Random selection at runtime (weighted: 70% common, 25% mid, 5% rare). Breaks pattern.

LDtk handles natively via Auto-Layer rules with variant frequency. Unity Tilemap: custom Rule Tile with random tiles.

Decoration overlays

Sparse decorative sprites (a flower, a crack, a leaf) painted ON TOP of the seamless tile layer. ~5% coverage. Massive perceived variety from small art investment.

Detail tiles

Tiles that look like the base interior but have a hand-painted detail (a vein in stone, a clump of grass). Insert occasionally. Same effect as decoration overlays but stays in the tilemap layer (cheaper for collision).

Transitional tiles

Where two terrains meet, paint:

• Edge (cardinal): grass→dirt N, E, S, W (4 + mirrors).
• Outer corner (convex): dirt poking into grass (4).
• Inner corner (concave): grass wrapping dirt (4).
• T-junction (3-way): grass on 3 sides (4) — often skipped.
• Cross (4-way): full surround (1) — often skipped.

47-tile RPGMaker schema covers all cases. 16-tile Wang skips diagonals (corner ambiguity).

For terrain hierarchy (grass < dirt < stone), one set of transitions between adjacent levels is enough; non-adjacent transitions (grass → stone) can compose grass→dirt + dirt→stone vertically.

Normal maps for 2D lighting

Normal maps add dynamic lighting to 2D sprites. Each pixel encodes a 3D surface normal in RGB:

• R = X-axis component
• G = Y-axis component
• B = Z-axis component
• Flat surface = (0.5, 0.5, 1.0) = #8080FF (purplish).

Authoring options:

Hand-painted (best quality)

Paint the normal map alongside the diffuse. Deep cyan = surface tilted left, deep magenta = right, green tints = up, purple = down. Time- consuming. Used in Owlboy, Dust: An Elysian Tail.

Sprite Lamp (semi-automatic)

You provide 3-4 lighting passes (top, right, etc.), tool generates normal map. ~$15. Quality very good.

Sprite DLight (procedural)

Just provide the diffuse. Tool generates a "good enough" normal from shape. Quick, less accurate.

Materialize (free, FOSS)

Generate normal + height + AO from a diffuse. Less specialized for pixel art but free.

NormalMap-Online / nlmtools

Quick browser-based gen.

Engine integration

• Unity URP 2D: assign Normal map secondary texture in Sprite Renderer. Light 2D respects it.
• Godot: shader on canvas item samples normal texture.
• Custom: standard tangent-space normal lighting.

Procedural + hand-pixel hybrid

For organic surfaces (rock, dirt, grass), efficient workflow:

1. Generate Perlin/Worley noise base in your tool of choice (Substance, Krita filter, Aseprite plugin, Filter Forge, hand-coded).
2. Crush the result into your palette (indexed mode → posterize).
3. Hand-paint over the result: clean up artifacts, add intentional features, define edges.
4. Apply offset-paint trick to make seamless.

Saves hours vs pure hand-paint. Looks more natural than pure procedural.

Specialized surfaces

Roof / shingle patterns

• Use staggered rows (alternating offset) for visual interest.
• Highlight edge of each shingle.
• 2-row tile (offset 0 + offset 16) seamless when stacked.

Floor / tile patterns

• Geometric grout lines OR organic stones.
• For geometric: ensure tile size is exact divisor of pattern (avoid mismatched alignment).
• Add wear/dirt overlay sparingly.

Wall patterns

• Often 9-slice candidate (corner stays, middle stretches).
• Or use vertical strip + repeat.
• Vary brick offset rows (running bond pattern).

Water / sky

• Animated 2-4 frame loop is more important than seamless.
• Subtle horizontal scroll of the texture creates drift effect.
• Layer 2-3 textures at different scroll speeds for parallax-ish water.

Common bugs

• Visible seam after offset: didn't fully cover the seam in step 3. Re-offset and check.
• Texture bleeding between tiles in atlas: solve with 1-2 px padding (TexturePacker --extrude, Aseprite Sprite Sheet export with padding).
• Normal map looks wrong direction: G channel inverted (DirectX vs OpenGL convention). Most engines have a flip toggle in Sprite Renderer.
• Atlas downscaling blurs tile edges: use POT atlases, nearest-neighbor sampling, no mipmaps for 2D pixel art.
• Variant frequency too high: dominant variant over 80% looks like no variation. Tune 60-70% for the "common" tile.
• Mirror seam visible in detailed textures: switch to offset-paint.

See also

• tile-design/SKILL.md
• lighting-art/SKILL.md — using normal maps in 2D Lights
• tools/SKILL.md — Aseprite, TexturePacker, Sprite Lamp