bmpimage.js

function BMPImage(w, h) {
  this.w = w;
  this.h = h;
  this.calc();
  this.data = new Array(this.h).fill("\0".repeat(this.row));
}

BMPImage.prototype.calc = function() {
 this.row = 4 * Math.ceil(this.w * 0.75);
 this.comp = this.row * this.h;
 this.size = this.comp + 54;
}

BMPImage.prototype.resize = function(w, h) {
 w = (w == null) ? this.w : w;
 h = (h == null) ? this.h : h;
 
 var oldrow = this.row;
 var oldh = this.h;
 
 this.w = w;
 this.h = h;
 this.calc();
 
 if (this.row > oldrow) {
  this.data = this.data.map(d => d + "\0".repeat(this.row - oldrow));
 }
 else if (this.row < oldrow) {
  this.data = this.data.map(d => d.substring(0, this.row));
 }
 if (this.h > oldh) {
  for (h = oldh; h < this.h; h++) {
   this.data.push("\0".repeat(this.row));
  }
 }
 else if (this.h < oldh) {
  for (h = oldh; h > this.h; h--) {
   this.data.pop();
  }
 }
}

BMPImage.prototype.chr = function(h, s) {
  var out = "";
  for (var i = 0; i < s; i++) {
    out += String.fromCharCode(h & 255);
    h >>= 8;
  }
  return out;
}

BMPImage.prototype.build = function() {
  return "data:image/bmp;base64," + btoa(["\x42\x4D",
    this.chr(this.size, 4),
    "\x00\x00\x00\x00\x36\x00\x00\x00\x28\x00\x00\x00",
    this.chr(this.w, 4),
    this.chr(this.h, 4),
    "\x01\x00\x18\x00\x00\x00\x00\x00",
    this.chr(this.comp, 4),
    "\x13\x0B\x00\x00\x13\x0B\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
  ].concat(this.data).join(""));
}

BMPImage.prototype.set = function(x, y, col) {
  var row = this.data[y % this.h];
  var addr = (x % this.w) * 3;
  this.data[y % this.h] = row.substring(0, addr) + this.chr(col[2], 1) + this.chr(col[1], 1) + this.chr(col[0], 1) + row.substring(addr + 3);
}

BMPImage.prototype.get = function(x, y) {
  var row = this.data[y % this.h];
  var addr = (x % this.w) * 3;
  return [row.charCodeAt(addr + 2), row.charCodeAt(addr + 1), row.charCodeAt(addr)];
}