Thanks for your help, Alfonse Reinheart! Both on the FBO and font size issues :)

For anyone stuck in similiar problems :

I add glReadBuffer(GL_NONE) when there are no draw buffers




//...

The code come from Martin Eisemann's sample project "Floating Texture",
everyone can use it under GPL: sourceforge.net/projects/floatingtexture/

I got VS 2010 as my Compiler&Linker, the external...