Arcball rotation around viewport-center

OpenGL OpenGL: Basic Coding
5

Ok, let’s think in eyepoint and origin.

  1. At the beginning (i.e. no arcball modifications) I want the origin to be located in: viewportwidth/2, viewportheight/2, 0. Eyepoint is origin but z-value > 0.
  2. The offset of the arcball should translate eye and origin only in x-y-direction.
  3. The rotation of the arcball should modify the eye, but not the origin.
    Is this clear to you?

To your last sentence: If I put the translate first in sequence I change the rotation-center. But of course you’re right about the concept.

EDIT: If you can compile my sample-project: There is almost everything correct; just the offset of the arcball is rotation-dependent.
EDIT2: I forgot to mention: I’ve found a site in this forum with the same problem (at least I think so). Unfortunatly the solution in this post doesn’t work.