title: OpenGL 4.2 use same texture as image and as sampler
body: <p>Is it legal (and well defined) to use the same texture as an image2D as well as a sampler2D?</p>
  
  <p>currently I use imageLoad() and imageStore() within the GLSL shader to write and load from a image2D. However, I would like to read (not write) also from some mipmap levels of the texture, but this is not supported by imageLoad (I think I would have to bind each mipMap level as a separate image2D but the ammount of available image units is quite limited). So my question is, whether it's ok to use the same texture which i use as a image2D for imageStore() also as a sampler2D to use with textureLod()?</p>