Silvio R. R. Sanches,  Ildelberto A. Rodello,  José R.F. Brega,  Antonio Carlos Sementille. 

Most available support tools and software libraries, in spite of satisfactorily estimating the position and orientation in which virtual objects are supposed to be generated, do not usually allow that real elements superimpose on virtual ones. In certain situations, the problem may cause an incoherent relation of depth between the virtual objects and the real elements of the scene. The present paper proposes both the organization and the exhibition in a coherent way of real and virtual elements in Mixed Reality environments, by using the chromakey technique and the OpenGL framebuffer manipulation functions.

http://www.lbd.dcc.ufmg.br/colecoes/svr/2008/004.pdf

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