do anyone ever create or know library for dynamic masking? hmm.. dynamic masking that i mean is like.. you render an object rotating with green bagckground, but you render it into a texture. than how to create a masking texture for that texture, so you can create the object appears in the screen but without the green background? the idea is just like at the movie creation when the camera tape people with green background, the at the movie we will see the people is walking at a cloud or ontop the sea. thx in advance.

Hail,
Even though I never tried that personally, but there are few ways that you could accomplish that.
The easiest way I believe it can be done pretty fast is to use fragment shader to sample your texture and discard the color Green.