[mattsp1290]

What

Adds a decoder-free way to import pixie's raster/Image API, plus an explicit ARMv6k portable-C guard. All changes are additive — import pixie and its full API are unchanged.

• src/pixie/images.nim — re-export chroma, so import pixie/images is a self-contained, decoder-free raster surface (rgbx/ColorRGBX available without a separate import chroma). pixie already re-exports chroma, so this is idempotent for import pixie.
• src/pixie/raster.nim (new) — convenience umbrella re-exporting images/paints/paths (+ chroma/vmath/bumpy). Decoder-free and font-free (omits contexts/fonts, which pull the font parsers).
• src/pixie/simd.nim — explicit else branch documenting that non-amd64/arm64 targets (32-bit ARM/ARMv6k devkitARM e.g. 3DS, PSP/Vita newlib) fall through to portable C on purpose, and warning future contributors not to add a bare elif defined(arm): that would silently capture ARMv6k. This documents existing behavior — the compiler emitted the same code before; no behavior change.
• tests/test_portable_raster.nim (new) — standalone regression test for the scalar path, run with -d:pixieNoSimd. Kept out of tests/tests.nim (which builds SIMD-on, so a per-file flag can't apply there).
• .github/workflows/build.yml — runs the portable test under -d:pixieNoSimd (C and C++).
• README.md — documents the decoder-free imports and portable-target support.

Why

import pixie unconditionally compiles the file-format decoders (PNG, JPEG, BMP, GIF, QOI, PPM, SVG) and zippy. On size-constrained, newlib-hosted targets like the Nintendo 3DS (ARMv6k) that only do CPU pixel math and never call readImage/writeFile, that's dead weight. Two consumers (shady's CPU shader-sim runtime and boxy/clckr) want the raster/Image surface without the decoders. This gives a narrow entry point without touching import pixie for existing users.

Verification

Host (arm64 macOS, Nim 2.2.10):

• ✅ import pixie/images and import pixie/raster nimcache is decoder-free (no png/jpeg/bmp/gif/qoi/svg/zippy/imagebase64); raster is also font-free.
• ✅ nim r tests/tests.nim — full existing suite green (import pixie unchanged).
• ✅ nim r -d:pixieNoSimd tests/test_portable_raster.nim — portable path passes (also under nim cpp, debug + release).
• ⚠️ nim cpp -r tests/tests.nim fails on this host with a pre-existing clang++ strictness issue in zippy (adler32_simd) + NEON SIMD (void*→typed pointer) — reproduced identically on clean master with these changes stashed, so it is not caused by this PR (Linux/gcc CI is unaffected).

On-device (ARMv6k / Nintendo 3DS, devkitARM):

• ✅ A minimal app importing pixie/raster cross-compiles with --define:ds3 --cpu:arm (the natural ARMv6k portable fall-through — not -d:pixieNoSimd, so it exercises this PR's new else branch for real) and links into a .3dsx.
• ✅ The -d:ds3 nimcache is decoder-free — the request's headline acceptance criterion — containing only chroma/blends and pixie/{blends,common,images,internal}. No png/jpeg/zippy/fileformats.
• The app prints PASS/FAIL for newImage, indexing, rgbx/ColorRGBX, .data, getRgbaSmooth, fill, draw to the top screen; the claim demonstrated is that the decoder-free raster surface executes correctly on ARMv6k (the guard itself is a no-op codification).

Companion chroma change

shady also depends on chroma for ColorRGBX + rgbx(uint8×4), both already in the zero-dependency chroma/colortypes. That is covered by birbparty/chroma#1 (comment/docs/CI-guard only — no code change), so no chroma pin is required for this PR. SHA 07a39f8c1cb9317ef70030894e5e4a59787fff7d is available to pin if ever wanted.

Scope notes

• requires "zippy" stays in pixie.nimble — full import pixie still needs it; the win is nimcache contents on a narrow import, not the dependency list.
• A -d:pixieNoFileFormats compile flag (to keep the literal import pixie spelling decoder-free) was considered but deferred — import pixie/images/pixie/raster already satisfy the consumers, and the flag is the more invasive change.

🤖 Generated with Claude Code

[mattsp1290]

✅ On-device confirmed. Ran the minimal import pixie/raster check app on physical Nintendo 3DS hardware (devkitARM .3dsx, built --define:ds3 --cpu:arm — the natural ARMv6k portable fall-through, not -d:pixieNoSimd):

RESULT: ALL CHECKS PASSED

All raster ops verified on-device: newImage / dimensions, indexing []=/[] + rgbx/ColorRGBX, fill + .data[], getRgbaSmooth, draw/blit. Combined with the decoder-free -d:ds3 nimcache (only chroma/blends + pixie/{blends,common,images,internal}), this demonstrates the decoder-free raster surface both builds lean and runs correctly on ARMv6k.