I don't think this is quite the same questions as this one but if you disagree feel free to close this :)
With SteamOS being announced yesterday I can see that it's entirely possible that opengl will get a big boost in usage in the near future. Now I already know direct3d11 quite well but I think maybe it's time to learn opengl too.
Are there any good resource for learning modern opengl that are aimed at programmers who already know direct3d11 pretty well. So don't need any education on the concepts and math, just on how to use the API and any important differences?