ReGBA by Nebuleon is a Game Boy Advance emulator based ultimately on gpSP 0.9 by Exophase. You can also submit patches on GitHub.

Release notes:

I’ve made ReGBA version 1.45.1 with two “rainbow fringe” subpixel scalers: kuwanger’s full-screen one and an aspect-ratio-preserving one based on it.

http://boards.dingoonity.org/gcw-releases/regba-gba-emulator-(alpha-1)/165/