2D FFT Plot

I am plotting the 2D FFT plot of a matrix

clc;clear all;close all;
format long;
f1= 128;f2=512; fs=2^12;
time=0:1/fs:1-(1/fs);
  D=8;
  var=5e-8;
  N=2^10;
  disp(fs/N);
  t=time(1:N);
  sig=sin(2*pi*f1*t);%+sin(2*pi*f2*t);
  x=sig+sqrt(var)*randn(size(t));
  x1=reshape(x,length(x)/D,D);
  xfft2=fftshift(fft2(winx));
  y=abs(xfft2);
  mesh(y);

The 2D FFT of this signal should be a sinc signal.Can anyone please explain why I am getting a triangular plot here?

[Akira Agata]

In your sample code, a variable winx seems undefined. Is this a typo of x1 ?