EdgeForge — Outline & Drop Shadow for Aseprite

Outlining a sprite by hand is fine once. It is not fine on the twelfth frame of a walk cycle.

EdgeForge adds an outline and/or a drop shadow to your art — painted onto new layers, so the original pixels are never modified, and the whole thing is one undo.

Corner control that actually matters

• Orthogonal — the crisp 4-way outline, no fattened corners
• Full 8-way — includes diagonals, reads heavier and rounder
• Diagonal only — for corner accents and chunkier retro looks
• Thickness 1–8, composed ring by ring so each layer of thickness is computed from the last complete ring — no smearing in the scan direction

Drop shadows

Any X/Y offset and colour, with alpha. The shadow is masked against the sprite itself, so it never paints over your art, and it clips cleanly at the canvas edge instead of wrapping.

It tells you when it would clip

If your outline would run off the canvas, EdgeForge says so rather than silently cropping the ring — the single most annoying way to lose ten minutes on this task.

Tested against real Aseprite

The geometry core has a headless suite covering corner modes, thickness composition, shadow masking, edge clipping and empty input. An end-to-end test then runs real Aseprite in batch mode and checks the outline lands on the right pixels — including with the source cel at an offset, since the mask has to be built in sprite space, not cel space — and that the source layer comes out untouched.

Install

Double-click the .aseprite-extension file, or Edit → Preferences → Extensions → Add. Requires Aseprite 1.3+.

Transparency: EdgeForge’s code is AI-assisted, disclosed via itch’s AI tagging. It generates no imagery — it only draws rings around the pixels you drew.