eShader(gl.VERTEX_SHADER);
   gl.shaderSource(vs, v);
   gl.compileShader(vs);
   
   var fs = gl.createShader(gl.FRAGMENT_SHADER);
   gl.shaderSource(fs, f);
   gl.compileShader(fs);
   
   var program = gl.createProgram();
   gl.attachShader(program, vs);
   gl.attachShader(program, fs);
   gl.linkProgram(program);
   
   // debug shader compile status
   var error = false;
   if (!gl.getShaderParameter(vs, gl.COMPILE_STATUS))
   {
      error = true;
      console.log(gl.getShaderInfoLo