Add a PNG writer so the demos produce actual images. Two pieces:
- src/jolt/png.janet — the encoder (8-bit RGB, filter None, stored/uncompressed
DEFLATE so no compressor is needed; correct CRC32 + Adler32). It lives in Janet
because per-byte work in the overlay is far too slow (a byte-array aset loop is
~30s for 360k bytes, and CRC32 over even a tiny image would be worse). Janet's
bit ops are 32-bit signed, so the 32-bit-unsigned arithmetic is done with plain
number ops (doubles hold 2^32) plus byte-level bxor. Exposed to the overlay as
janet.png/* by importing it into eval_base's module-load-env.
- src/jolt/jolt/png.clj — the jolt.png overlay wrapper: image / put! / write. The
overlay only produces pixels; the host encodes them in one pass.
mandelbrot gets a `render` subcommand (jolt -m mandelbrot render out.png [size])
that colours count-point's escape counts; the numeric-arg bench path is untouched.
Verified end to end: macOS `sips` accepts the output (so CRC/zlib are valid).
png-test covers the encoder structure (signature/IHDR/IEND) and the overlay
round-trip.
Co-authored-by: Yogthos <yogthos@gmail.com>
