function tgaHeader
tgaHeader(): Coder<TgaHeader>

Creates a coder for a Truevision TGA image header.

The imageId field's length is derived from idLength, so a header with no image ID needs idLength = 0 and an empty imageId.

Nothing beyond the header and image ID is parsed — the color map, pixel data, and TGA 2.0 footer/extension area are all left to the caller. Nothing is validated on encode either: idLength is written exactly as given, so it must match imageId.length.

Examples

Header carrying an image ID

import { assertEquals } from "@std/assert";
import { tgaHeader, TGA_HEADER_SIZE, TGA_IMAGE_TYPE } from "@binstruct/tga";

const imageId = new TextEncoder().encode("frame01");
const coder = tgaHeader();
const header = {
  idLength: imageId.length,
  colorMapType: 0,
  imageType: TGA_IMAGE_TYPE.grayscale,
  colorMapFirstEntryIndex: 0,
  colorMapLength: 0,
  colorMapEntrySize: 0,
  xOrigin: 0,
  yOrigin: 0,
  width: 16,
  height: 16,
  pixelDepth: 8,
  imageDescriptor: 0,
  imageId,
};

const buffer = new Uint8Array(64);
const written = coder.encode(header, buffer);
const [decoded, read] = coder.decode(buffer.subarray(0, written));

assertEquals(written, TGA_HEADER_SIZE + imageId.length);
assertEquals(read, written);
assertEquals(decoded.imageId, imageId);
assertEquals(decoded.idLength, imageId.length);

Known wire bytes for a color-mapped image

import { assertEquals } from "@std/assert";
import { tgaHeader, TGA_IMAGE_TYPE } from "@binstruct/tga";

// deno-fmt-ignore
const wire = new Uint8Array([
  0x00,             // idLength = 0
  0x01,             // colorMapType = 1 (present)
  0x01,             // imageType = colorMapped
  0x00, 0x00,       // colorMapFirstEntryIndex = 0
  0x00, 0x01,       // colorMapLength = 256
  0x18,             // colorMapEntrySize = 24
  0x00, 0x00,       // xOrigin = 0
  0x00, 0x00,       // yOrigin = 0
  0x0a, 0x00,       // width = 10
  0x0a, 0x00,       // height = 10
  0x08,             // pixelDepth = 8
  0x00,             // imageDescriptor = 0
]);

const [decoded, read] = tgaHeader().decode(wire);

assertEquals(read, wire.length);
assertEquals(decoded.imageType, TGA_IMAGE_TYPE.colorMapped);
assertEquals(decoded.colorMapLength, 256);
assertEquals(decoded.width, 10);
assertEquals(decoded.height, 10);
assertEquals(decoded.imageId.length, 0);

Return Type

Coder<TgaHeader>

A coder for TgaHeader values.

Usage

import { tgaHeader } from ".";