alpha_composite — GFX2D composite op

• Data kinds: rgba × rgba → rgba

• Call: import gfx2d; gfx2d.alpha_composite(src, dst) (or opsgfx2d.get("alpha_composite"))

Usage

Porter–Duff over on straight-alpha `rgba` (Porter & Duff 1984).

`a_o = a_s + a_d (1 - a_s)` and

`C_o = (C_s a_s + C_d a_d (1 - a_s)) / a_o, with C_o = 0` where

`a_o == 0`.

Both arguments must be straight-alpha and the same shape — this family

never broadcasts, because a broadcast image is a silently wrong picture. Use

:func:sprite_blit to place something smaller.

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• gfx2d_scene — py -3.11 examples/gfx2d_scene.py

Ops the type connects to (they accept rgba as input)

premultiply · sprite_blit · sprite_transform · sprite_sheet_slice · nine_slice

Same category (composite)

premultiply · unpremultiply · alpha_composite_premul · blend_mode · layer_stack

*Provenance: gfx2d.py — GFX2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.