threejs/manual/examples/resources/lut-reader.js

function splitOnSpaceHandleQuotesWithEscapes(str, splits = ' \t\n\r') {
  const strings = [];
  let quoteType;
  let escape;
  let s = [];
  for (let i = 0; i < str.length; ++i) {
    const c = str[i];
    if (escape) {
      escape = false;
      s.push(c);
    } else {
      if (quoteType) {  // we're inside quotes
        if (c === quoteType) {
          quoteType = undefined;
          strings.push(s.join(''));
          s = [];
        } else if (c === '\\') {
          escape = true;
        } else {
          s.push(c);
        }
      } else {  // we're not in quotes
        if (splits.indexOf(c) >= 0) {
          if (s.length) {
            strings.push(s.join(''));
            s = [];
          }
        } else if (c === '"' || c === '\'') {
          if (s.length) {  // its in th middle of a word
            s.push(c);
          } else {
            quoteType = c;
          }
        } else {
          s.push(c);
        }
      }
    }
  }
  if (s.length || strings.length === 0) {
    strings.push(s.join(''));
  }
  return strings;
}

const startWhitespaceRE = /^\s/;
const intRE = /^\d+$/;
const isNum = s => intRE.test(s);

const quotesRE = /^".*"$/;
function trimQuotes(s) {
  return quotesRE.test(s) ? s.slice(1, -1) : s;
}

const splitToNumbers = s => s.split(' ').map(parseFloat);

export function parseCSP(str) {
  const data = [];
  const lut = {
    name: 'unknown',
    type: '1D',
    size: 0,
    data,
    min: [0, 0, 0],
    max: [1, 1, 1],
  };

  const lines = str.split('\n').map(s => s.trim()).filter(s => s.length > 0 && !startWhitespaceRE.test(s));

  // check header
  lut.type = lines[1];
  if (lines[0] !== 'CSPLUTV100' ||
       (lut.type !== '1D' && lut.type !== '3D')) {
    throw new Error('not CSP');
  }

  // skip meta (read to first number)
  let lineNdx = 2;
  for (; lineNdx < lines.length; ++lineNdx) {
    const line = lines[lineNdx];
    if (isNum(line)) {
      break;
    }
    if (line.startsWith('TITLE ')) {
      lut.name = trimQuotes(line.slice(6).trim());
    }
  }

  // read ranges
  for (let i = 0; i < 3; ++i) {
    ++lineNdx;
    const input = splitToNumbers(lines[lineNdx++]);
    const output = splitToNumbers(lines[lineNdx++]);
    if (input.length !== 2 || output.length !== 2 ||
        input[0] !== 0 || input[1] !==  1 ||
        output[0] !== 0 || output[1] !== 1) {
      throw new Error('mapped ranges not support');
    }
  }

  // read sizes
  const sizes = splitToNumbers(lines[lineNdx++]);
  if (sizes[0] !== sizes[1] || sizes[0] !== sizes[2]) {
    throw new Error('only cubic sizes supported');
  }
  lut.size = sizes[0];

  // read data
  for (; lineNdx < lines.length; ++lineNdx) {
    const parts = splitToNumbers(lines[lineNdx]);
    if (parts.length !== 3) {
      throw new Error('malformed file');
    }
    data.push(...parts);
  }

  return lut;
}

export function parseCUBE(str) {
  const data = [];
  const lut = {
    name: 'unknown',
    type: '1D',
    size: 0,
    data,
    min: [0, 0, 0],
    max: [1, 1, 1],
  };

  const lines = str.split('\n');
  for (const origLine of lines) {
    const hashNdx = origLine.indexOf('#');
    const line = hashNdx >= 0 ? origLine.substring(0, hashNdx) : origLine;
    const parts = splitOnSpaceHandleQuotesWithEscapes(line);
    switch (parts[0].toUpperCase()) {
      case 'TITLE':
        lut.name = parts[1];
        break;
      case 'LUT_1D_SIZE':
        lut.size = parseInt(parts[1]);
        lut.type = '1D';
        break;
      case 'LUT_3D_SIZE':
        lut.size = parseInt(parts[1]);
        lut.type = '3D';
        break;
      case 'DOMAIN_MIN':
        lut.min = parts.slice(1).map(parseFloat);
        break;
      case 'DOMAIN_MAX':
        lut.max = parts.slice(1).map(parseFloat);
        break;
      default:
        if (parts.length === 3) {
          data.push(...parts.map(parseFloat));
        }
        break;
    }
  }

  if (!lut.size) {
    lut.size = lut.type === '1D'
        ? (data.length / 3)
        : Math.cbrt(data.length / 3);
  }

  return lut;
}

function lerp(a, b, t) {
  return a + (b - a) * t;
}

function lut1Dto3D(lut) {
  let src = lut.data;
  if (src.length / 3 !== lut.size) {
    src = [];
    for (let i = 0; i < lut.size; ++i) {
      const u = i / lut.size * lut.data.length;
      const i0 = (u | 0) * 3;
      const i1 = i0 + 3;
      const t = u % 1;
      src.push(
        lerp(lut.data[i0 + 0], lut.data[i1 + 0], t),
        lerp(lut.data[i0 + 0], lut.data[i1 + 1], t),
        lerp(lut.data[i0 + 0], lut.data[i1 + 2], t),
      );
    }
  }
  const data = [];
  for (let i = 0; i < lut.size * lut.size; ++i) {
    data.push(...src);
  }
  return {...lut, data};
}

const parsers = {
  'cube': parseCUBE,
  'csp': parseCSP,
};

// for backward compatibility
export function parse(str, format = 'cube') {
  const parser = parsers[format.toLowerCase()];
  if (!parser) {
    throw new Error(`no parser for format: ${format}`);
  }
  return parser(str);
}

export function lutTo2D3Drgba8(lut) {
  if (lut.type === '1D') {
    lut = lut1Dto3D(lut);
  }
  const {min, max, size} = lut;
  const range = min.map((min, ndx) => {
    return max[ndx] - min;
  });
  const src = lut.data;
  const data = new Uint8Array(size*size*size * 4);
  const srcOffset = (offX, offY, offZ) => {
    return (offX + offY * size + offZ * size * size) * 3;
  };
  const dOffset = (offX, offY, offZ) => {
    return (offX + offY * size + offZ * size * size) * 4;
  };
  for (let dz = 0; dz < size; ++dz) {
    for (let dy = 0; dy < size; ++dy) {
      for (let dx = 0; dx < size; ++dx) {
        const sx = dx;
        const sy = dz;
        const sz = dy;
        const sOff = srcOffset(sx, sy, sz);
        const dOff = dOffset(dx, dy, dz);
        data[dOff + 0] = (src[sOff + 0] - min[0]) / range[0] * 255;
        data[dOff + 1] = (src[sOff + 1] - min[1]) / range[1] * 255;
        data[dOff + 2] = (src[sOff + 2] - min[2]) / range[2] * 255;
        data[dOff + 3] = 255;
      }
    }
  }
  return {...lut, data};
}