toot medias: extract color from blurhash

src/platform/blurhash.ts

@@ -0,0 +1,164 @@
+/*
+Blurhash toolkit.
+
+base83 decoder/encoder is copied from
+https://github.com/woltapp/blurhash/blob/master/TypeScript/src/base83.ts,
+which is MIT Licensed: https://github.com/woltapp/blurhash?tab=MIT-1-ov-file#readme
+*/
+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",
+  "#",
+  "$",
+  "%",
+  "*",
+  "+",
+  ",",
+  "-",
+  ".",
+  ":",
+  ";",
+  "=",
+  "?",
+  "@",
+  "[",
+  "]",
+  "^",
+  "_",
+  "{",
+  "|",
+  "}",
+  "~",
+];
+
+function decode83(str: string) {
+  let value = 0;
+  for (let i = 0; i < str.length; i++) {
+    const c = str[i];
+    const digit = digitCharacters.indexOf(c);
+    value = value * 83 + digit;
+  }
+  return value;
+}
+
+function encode83(n: number, length: number): string {
+  var result = "";
+  for (let i = 1; i <= length; i++) {
+    let digit = (Math.floor(n) / Math.pow(83, length - i)) % 83;
+    result += digitCharacters[Math.floor(digit)];
+  }
+  return result;
+}
+
+/* toColorHex() is modified from
+https://www.xaymar.com/articles/2020/12/08/fastest-uint8array-to-hex-string-conversion-in-javascript/,
+licensed BSD-3. */
+
+// Pre-Init
+const LUT_HEX_4b = [
+  "0",
+  "1",
+  "2",
+  "3",
+  "4",
+  "5",
+  "6",
+  "7",
+  "8",
+  "9",
+  "A",
+  "B",
+  "C",
+  "D",
+  "E",
+  "F",
+];
+const LUT_HEX_8b = new Array(0x100);
+for (let n = 0; n < 0x100; n++) {
+  LUT_HEX_8b[n] = `${LUT_HEX_4b[(n >>> 4) & 0xf]}${LUT_HEX_4b[n & 0xf]}`;
+}
+// End Pre-Init
+function toColorHex(buffer: Uint8ClampedArray): `#${string}` {
+  let out = "#";
+  for (let idx = 0, edx = buffer.length; idx < edx; idx++) {
+    out += LUT_HEX_8b[buffer[idx]];
+  }
+  return out as `#${string}`;
+}
+
+export function averageColor(blurhash: string) {
+  const v = decode83(blurhash.substring(2, 6)); // 24-bit RGB
+
+  return [v >> 16, (v >> 8) & 255, v & 255] as const;
+}
+
+export function averageColorHex(blurhash: string) : `#${string}` {
+  const [r, g, b] = averageColor(blurhash);
+
+  const buf = new Uint8ClampedArray(3);
+  buf[0] = r;
+  buf[1] = g;
+  buf[2] = b;
+
+  return toColorHex(buf);
+}