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Convert blurhash to a base64 DataURL string (no canvas or node-canvas)
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| import { decode } from 'blurhash'; | |
| // source of code below https://github.com/wheany/js-png-encoder/blob/master/generatepng.js | |
| const DEFLATE_METHOD = String.fromCharCode(0x78, 0x01); | |
| const CRC_TABLE: number[] = []; | |
| const SIGNATURE = String.fromCharCode(137, 80, 78, 71, 13, 10, 26, 10); | |
| const NO_FILTER = String.fromCharCode(0); | |
| const makeCrcTable = () => { | |
| let c; | |
| for (let n = 0; n < 256; n++) { | |
| c = n; | |
| for (let k = 0; k < 8; k++) { | |
| if (c & 1) { | |
| c = 0xedb88320 ^ (c >>> 1); | |
| } else { | |
| c = c >>> 1; | |
| } | |
| } | |
| CRC_TABLE[n] = c; | |
| } | |
| }; | |
| makeCrcTable(); | |
| const inflateStore = (data: string) => { | |
| const MAX_STORE_LENGTH = 65535; | |
| let storeBuffer = ''; | |
| let remaining; | |
| let blockType; | |
| for (let i = 0; i < data.length; i += MAX_STORE_LENGTH) { | |
| remaining = data.length - i; | |
| blockType = ''; | |
| if (remaining <= MAX_STORE_LENGTH) { | |
| blockType = String.fromCharCode(0x01); | |
| } else { | |
| remaining = MAX_STORE_LENGTH; | |
| blockType = String.fromCharCode(0x00); | |
| } | |
| // little-endian | |
| storeBuffer += blockType + String.fromCharCode(remaining & 0xff, (remaining & 0xff00) >>> 8); | |
| storeBuffer += String.fromCharCode(~remaining & 0xff, (~remaining & 0xff00) >>> 8); | |
| storeBuffer += data.substring(i, i + remaining); | |
| } | |
| return storeBuffer; | |
| }; | |
| const adler32 = (data: string) => { | |
| const MOD_ADLER = 65521; | |
| let a = 1; | |
| let b = 0; | |
| for (let i = 0; i < data.length; i++) { | |
| a = (a + data.charCodeAt(i)) % MOD_ADLER; | |
| b = (b + a) % MOD_ADLER; | |
| } | |
| return (b << 16) | a; | |
| }; | |
| const updateCrc = (crc: number, buf: string) => { | |
| let c = crc; | |
| let b: number; | |
| for (let n = 0; n < buf.length; n++) { | |
| b = buf.charCodeAt(n); | |
| c = CRC_TABLE[(c ^ b) & 0xff] ^ (c >>> 8); | |
| } | |
| return c; | |
| }; | |
| const crc = (buf: string) => updateCrc(0xffffffff, buf) ^ 0xffffffff; | |
| const dwordAsString = (dword: number) => | |
| String.fromCharCode( | |
| (dword & 0xff000000) >>> 24, | |
| (dword & 0x00ff0000) >>> 16, | |
| (dword & 0x0000ff00) >>> 8, | |
| dword & 0x000000ff, | |
| ); | |
| const createChunk = (length: number, type: string, data: string) => { | |
| const CRC = crc(type + data); | |
| return dwordAsString(length) + type + data + dwordAsString(CRC); | |
| }; | |
| const IEND = createChunk(0, 'IEND', ''); | |
| const createIHDR = (width: number, height: number) => { | |
| const IHDRdata = | |
| dwordAsString(width) + | |
| dwordAsString(height) + | |
| // bit depth | |
| String.fromCharCode(8) + | |
| // color type: 6=truecolor with alpha | |
| String.fromCharCode(6) + | |
| // compression method: 0=deflate, only allowed value | |
| String.fromCharCode(0) + | |
| // filtering: 0=adaptive, only allowed value | |
| String.fromCharCode(0) + | |
| // interlacing: 0=none | |
| String.fromCharCode(0); | |
| return createChunk(13, 'IHDR', IHDRdata); | |
| }; | |
| const png = (width: number, height: number, rgba: Uint8ClampedArray) => { | |
| const IHDR = createIHDR(width, height); | |
| let scanlines = ''; | |
| for (let y = 0; y < rgba.length; y += width * 4) { | |
| scanlines += NO_FILTER; | |
| for (let x = 0; x < width * 4; x++) { | |
| scanlines += String.fromCharCode(rgba[y + x] & 0xff); | |
| } | |
| } | |
| const compressedScanlines = | |
| DEFLATE_METHOD + inflateStore(scanlines) + dwordAsString(adler32(scanlines)); | |
| const IDAT = createChunk(compressedScanlines.length, 'IDAT', compressedScanlines); | |
| return SIGNATURE + IHDR + IDAT + IEND; | |
| }; | |
| // this is a fork of https://gist.github.com/mattiaz9/53cb67040fa135cb395b1d015a200aff | |
| const getPngArray = (pngString: string) => { | |
| const pngArray = new Uint8Array(pngString.length); | |
| for (let i = 0; i < pngString.length; i++) { | |
| pngArray[i] = pngString.charCodeAt(i); | |
| } | |
| return pngArray; | |
| }; | |
| const blurHashToDataURL = (hash: string, width = 32, height = 32) => { | |
| const rgba = decode(hash, width, height); | |
| const pngString = png(width, height, rgba); | |
| const base64 = | |
| typeof window === 'undefined' | |
| ? Buffer.from(getPngArray(pngString)).toString('base64') | |
| : btoa(pngString); | |
| return `data:image/png;base64,${base64}`; | |
| }; | |
| export { blurHashToDataURL }; |
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thanks for this - just a note, line 148 may have a typo:
decode(hash, width, width);instead ofdecode(hash, width, height);