epng.js

class ePNG {
   constructor(data, w, h){
      if(data.length != (w * h * 4)) return console.error(`Corrupted samples.`);
      this.buffer = new Uint8Array(w * h * 4 + h);
      for(let i = 0; i < h; i++){
         this.buffer.set(data.slice(i * w * 4, (i + 1) * w * 4), i * w * 4 + 1 + i);
      }
      this.makeCRCTable();
      this.ihdr = new Uint8Array([0, 0, 0, 13, 73, 72, 68, 82, ...this.set32bit(w), ...this.set32bit(h), 8, 6, 0, 0, 0, 0, 0, 0, 0]);
      this.ihdr.set(this.getCRC32(this.ihdr.slice(4, 21)), 21);
   }
   set32bit(v){
     return [v >> 24 & 255, v >> 16 & 255, v >> 8 & 255, v & 255];
   }
   makeCRCTable(){
      let c, a = [];
      for(let n = 0; n < 256; n++){
         c = n;
         for(let k = 0; k < 8; k++){
            c = c & 1 ? 0xEDB88320 ^ c >>> 1 : c >>> 1;
         }
         a.push(c);
      }
      this.crcTable = a;
   }
   getCRC32(data){
      let crc = -1;
      data.map(v => crc = crc >>> 8 ^ this.crcTable[(crc ^ v) & 255]);
      return this.set32bit(crc ^ -1 >>> 0);
   }
   compress(input){
     let cs = new CompressionStream('deflate');
     let writer = cs.writable.getWriter();
     writer.write(input);
     writer.close();
     return new Response(cs.readable).bytes();
   }
   encode(){
      return new Promise((resolve, reject) => {
         this.compress(this.buffer).then(c => {            
            let idat = new Uint8Array([...this.set32bit(c.length), 73, 68, 65, 84, ...c, ...this.getCRC32([73, 68, 65, 84, ...c])]);
            resolve(new Blob([new Uint8Array([137, 80, 78, 71, 13, 10, 26, 10]), this.ihdr, idat, new Uint8Array([0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130])], {type: "image/png"}));
         });
      });
   }
}
/* EXEMPLO DE USO
window.addEventListener('load', e => {
   let colors = [], d = [];
   for(let c = 0; c < 256; c++) colors.push([parseInt(Math.random() * 255, 10), parseInt(Math.random() * 255, 10), parseInt(Math.random() * 255, 10), 255]);
   for(let i = 0; i < 500; i++){
      let color = parseInt(Math.random() * 255, 10);
      for(let j = 0; j < 500; j++){
         d.push(...colors[color]);
      }
   }
   let t0 = Date.now();
   png = new ePNG(d, 500, 500);
   png.encode().then(b => {
      let url = window.URL.createObjectURL(b);
      document.body.innerHTML += `<br><hr><br><br><span>Tamanho: ${parseInt(b.size / 1024, 10)} KB</span><br><span>Tempo decorrido: ${Date.now() - t0} milissegundos</span><br><img src="${url}">`;
   });
});
*/