Perfect (3D) texture mapping in opengl

Question

I am trying to create a simple 3D-array visualisation in opengl. The 3D-array contains color values. To achieve this, I could just draw lots of cubes, giving them texture-co

Answer 1

Can anyone tell me how to handle this?

You're running into the infamous fenceposting problem. Simply spoken, texture coordinates 0 and 1 are not pixel centers, but pixel borders. Have a look at this simple sketch

  | 0 | 1 | 2 | 3 |
  ^               ^
 0.0             1.0

  0   1   2   3   4
 --- --- --- --- ---
  4   4   4   4   4

So to address pixel i (say 0) of a texture N (say 4) pixels wide you must use the texture coordinate

(i/N + (i+1)/N)/2 = i/2N + (i+1)/2N = (2i + 1) / 2N = (i + 0.5)/N

So adding that 0.5 is not a hack. However in the shader you can just use texelFetch to address the texture in absolute pixels, instead of a sampling coordinate. However you must implement filtering yourself then.