ABSTRACT
This chapter approaches the end of the rendering pipeline. Its last stage is the output merger. As is the rasterizer, the output merger is hard-wired but controllable through GL commands. The chapter focuses on two main functionalities of the output merger: z-buffering and alpha blending. The method of determining visible surfaces is named z-buffering or depth buffering. In principle, z-buffering allows primitives to be processed in an arbitrary order. It is one of the key features making the method so popular. Even though z-buffering generally allows the primitives to be processed in an arbitrary order, it does not apply to translucent primitives. The blending process uses the alpha value of the fragment, often called the alpha channel and is named alpha blending. The alpha channel typically contains as many bits as a color channel.
