I posted the newest OpenGL error (with this "not found") on main Ruby forum. Maybe they know how to fix it. The real problem is, that this solution poster previously is not working for Ruby 1.9.2. So I installed Ruby 1.9.1 and it's now working.
This time I made mirrors. I needed this OpenGL for running DevIL. I changed the screenshot method to able setting width.
This line: $screen.screenshot(width=[81920-$game.scx,768].min).to_gosu($screen).draw(81920-$game.scx+width,576,0,-1,-1) makes screenshot each frame, changes to Gosu image and draws in specified place. Effect is awesome: http://img406.imageshack.us/img406/7530/mirror.png
But I'm writting this because of some problem (I'm putting aside awful lags). I just started using DevIL/OpenGL, maybe I'm doing something wrong, or it's this library's issue. It's showed on the screenshot above: the mirror is drawn on the top. No matter how Z I type, it covers everything. And I don't know what's wrong.
And another problem I probably had with TexPlay in my previous project. I used it to make lights, but drew some time, it was making the game crash. I figured why (this time with DevIL): these screenshots in each frame are using more and more memory (RAM). After some time, game just stops and crashes. I don't know so much TexPlay or DevIL to realise why is it happening.