How the GBA + Gen III Decomp Tileset System Works

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This page covers GBA hardware and Gen III decomp fundamentals for users new to tilesets:

  • 8x8 tiles, 4bpp indexed color, palette slots 0–15 with slot 0 as transparency

  • Metatiles: 16x16 composites of 8x8 subtiles (2x2 tiles); tilemap entries (tile index + palette index + flip flags)

  • Metatile dual vs triple layer concept

  • Primary vs secondary tilesets: tile count limits, palette allocation (primary gets palettes 0–5, secondary gets 6–12 in default emerald)

  • The fieldmap.h constants and what they control at a high level

  • Artifact files: tiles.png, palettes/*.pal, metatiles.bin, metatile_attributes.bin

  • How Porymap fits in as the visual editor — Porytiles + Porymap together are a complementary “super suite” of tools, and Porytiles is designed with this in mind

Cross-references: Configuration Reference for fieldmap constants, Metatile Attributes Reference for attribute details