src/format-readers/exp.js


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import { stitchTypes } from "../file-renderer/pattern";

function expDecode(input) {
  return input > 128 ? -(~input & 255) - 1 : input;
}

export function expRead(file, pattern) {
  let b0 = 0,
    b1 = 0,
    dx = 0,
    dy = 0,
    flags = 0,
    i = 0,
    byteCount = file.byteLength;
  while (i < byteCount) {
    flags = stitchTypes.normal;
    b0 = file.getInt8(i);
    i += 1;
    b1 = file.getInt8(i);
    i += 1;
    if (b0 === -128) {
      if (b1 & 1) {
        b0 = file.getInt8(i);
        i += 1;
        b1 = file.getInt8(i);
        i += 1;
        flags = stitchTypes.stop;
      } else if (b1 === 2 || b1 === 4) {
        b0 = file.getInt8(i);
        i += 1;
        b1 = file.getInt8(i);
        i += 1;
        flags = stitchTypes.trim;
      } else if (b1 === -128) {
        b0 = file.getInt8(i);
        i += 1;
        b1 = file.getInt8(i);
        i += 1;
        b0 = 0;
        b1 = 0;
        flags = stitchTypes.trim;
      }
    }
    dx = expDecode(b0);
    dy = expDecode(b1);
    pattern.addStitchRel(dx, dy, flags, true);
  }
  pattern.addStitchRel(0, 0, stitchTypes.end);
  pattern.invertPatternVertical();
}