react-native-blurhash/lib/module/utils.js

🖼 Blurhash is a compact representation of a placeholder for an image. This is a Native UI Module for React Native to asynchronously wrap the Blurhash implementations and make them usable in React Native. Also supports encoding!

// Some functions from the Blurhash JS implementation that are used for light tasks (such as getting the average color or validating if a blurhash string is valid)

function sRGBToLinear(value) {
  const v = value / 255;
  if (v <= 0.04045) return v / 12.92;else return Math.pow((v + 0.055) / 1.055, 2.4);
}
export function decodeDC(value) {
  const intR = value >> 16;
  const intG = value >> 8 & 255;
  const intB = value & 255;
  return {
    r: sRGBToLinear(intR) * 255,
    g: sRGBToLinear(intG) * 255,
    b: sRGBToLinear(intB) * 255
  };
}
export function decode83(str) {
  let value = 0;
  for (let i = 0; i < str.length; i++) {
    const c = str[i];
    const digit = digitCharacters.indexOf(c);
    value = value * 83 + digit;
  }
  return value;
}
function validateBlurhash(blurhash) {
  if (!blurhash || blurhash.length < 6) throw new Error('The blurhash string must be at least 6 characters');
  const sizeFlag = decode83(blurhash[0]);
  const numY = Math.floor(sizeFlag / 9) + 1;
  const numX = sizeFlag % 9 + 1;
  if (blurhash.length !== 4 + 2 * numX * numY) throw new Error(`blurhash length mismatch: length is ${blurhash.length} but it should be ${4 + 2 * numX * numY}`);
}
export function isBlurhashValid(blurhash) {
  try {
    validateBlurhash(blurhash);
  } catch (error) {
    const message = error instanceof Error ? error.message : JSON.stringify(error);
    return {
      isValid: false,
      errorReason: message
    };
  }
  return {
    isValid: true
  };
}
const digitCharacters = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '#', '$', '%', '*', '+', ',', '-', '.', ':', ';', '=', '?', '@', '[', ']', '^', '_', '{', '|', '}', '~'];
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