images/ppm

PPM (Portable Pixmap, P6) encode + decode.

1 file lib/images/ppm/ppm.vader 5 exports

Converts between a raw byte stream in the binary P6 format and a structured Ppm value. P6 is an ASCII header (P6 width height maxval) followed by the raw RGB raster: 3 samples per pixel, row-major, top-to-bottom. A sample is 1 byte when maxval < 256 (8-bit) and 2 bytes, most-significant byte first (big-endian), when maxval >= 256 (16-bit). pixels always holds the raster exactly as it appears on disk, so encode/decode round-trip byte-for-byte and the 16-bit byte order is preserved without reinterpretation.

Scope: P6 binary only (no P3 ASCII variant). The header may carry # comment lines between tokens, per the netpbm spec.

Types

Ppm

struct ppm.vader:19

Ppm :: struct

An RGB pixmap decoded from / to be encoded as binary PPM (P6).

Fields

width: u32

No description.

height: u32

No description.

maxval: u32

Maximum sample value, in 1..=65535. < 256 ⇒ 8-bit (1 byte/sample), otherwise 16-bit (2 bytes/sample, most-significant byte first).

pixels: u8[]

Raw raster, row-major, exactly as stored on disk: width*height*3 bytes when 8-bit, width*height*6 (MSB-first pairs) when 16-bit.

Implements Display to_string :: fn(self) -> string

PpmError

struct ppm.vader:32

PpmError :: struct

Error raised by decode (malformed stream) or encode (inconsistent Ppm).

Fields

msg: string

No description.

Implements Error message :: fn(self) -> string

Functions

bytes_per_sample

fn ppm.vader:43

bytes_per_sample :: fn(maxval: u32) -> i64

Bytes per colour sample for a given maxval: 1 when maxval < 256, else 2. Exposed so callers can index Ppm.pixels correctly for 16-bit images.

Parameters

maxval u32 the image's maximum sample value.

Returns

i64

decode

fn ppm.vader:117

decode :: fn(data: u8[]) -> Ppm | PpmError

Decode a binary P6 PPM byte stream into a Ppm.

Validates the P6 magic, parses the width height maxval header (skipping whitespace and # comments), consumes exactly one whitespace byte after maxval, and checks the remaining raster length against width * height * 3 * bytes_per_sample(maxval). pixels is an owned copy of that raster.

Parameters

data u8[] the full P6 byte stream.

Returns

Ppm | PpmError the decoded Ppm on success.

Errors

PpmError on a bad magic, a missing/invalid header integer, a maxval outside 1..=65535, a missing whitespace after maxval, or a raster whose length disagrees with the header.

encode

fn ppm.vader:164

encode :: fn(img: Ppm) -> u8[] | PpmError

Encode a Ppm as a binary P6 byte stream (ASCII header + raw raster).

Parameters

img Ppm the image to encode ; img.pixels.len() must equal width * height * 3 * bytes_per_sample(maxval).

Returns

u8[] | PpmError the P6 byte stream.

Errors

PpmError when maxval is outside 1..=65535, or when pixels.len() disagrees with the dimensions.