This recipe implements a binocular view effect, where a scene is rendered as if it's visualized from the binocular itself. We will implement this effect by programing a procedural shader. Alternatively, in another technique, the alpha-mapped texture is used instead. In this approach, an alpha-masked texture containing a binocular view image is superimposed on top of the scene. This way, only those parts of the scene are visible that belong to the nonmasked texture region.

The procedural textured approach is also relatively simpler. Here, the scene is programmed in the fragment shader where the binocular view effect is created using texture coordinates of the vertices. Texture coordinates are used to create a logical circular region on the rendered image. The fragment that belongs outside the circumference of this circular region are rendered with an opaque color (say black). This opacity reduces as the distance shrinks toward the center...