From the OpenGL Blue Book, the glTexEnvi() function definition is the following: void glTexEnvi(GLenum target, GLenum pname, GLint param) PARAMETERS . . . param - Specifies a single symbolic constant, one of GL_MODULATE, GL_DECAL, or GL_BLEND. but in the book "OpenGL Game Programming, I see glTexEnvi() used with GL_REPLACE in the "param" parameter lots of times. The first time I noticed it, I thought "that''s probably an error, if I check the source it should be corrected" and so I did... but it was just the same as in the book. And when I tried to compile it, I expected an error but it runs just fine! Can someone explain me why and what does that parameter do? Thanks Raúl