title: glReadPixels returns wrong values
body: <p>I try to get rendered pixels color.</p>
  
  <pre><code>gl.glColor3f(1f, 0, 0);
  //draw
  gl.glReadPixels(lastX - pw / 2, MyCanvas.this.getHeight()
              - (lastY - ph / 2), pw, ph, GL.GL_RED, GL.GL_FLOAT,
              pixelBuffer);
  float r, g, b;
  r = pixelBuffer.getFloat();
  g = pixelBuffer.getFloat();
  b =pixelBuffer.getFloat();
  pixelBuffer.rewind();
  System.out.println(r+" "+g+" "+b);
  </code></pre>
  
  <p>there is real pure red color on the screen, but glReadPixels returns to the r very strange value 4.6006E-41, why???</p>