Backface Culling

The term Back Face Culling refers to a technique of 3D computer graphics, with a majority of non-visible triangles ( or more generally of polygons ) of a scene is removed. Thereby, the rendering speed is increased. In a triangle one of the two sides defined by the normal vector as the front side.

If there is only closed, massive objects in the scene, the viewer always look back on those fronts.

In a cube, for example, up to 3 pages simultaneously visible (the other side facing away from the viewer ). It is therefore unnecessary to draw the backs (English back faces ) ( since they are so obscured by other triangles ).

So let us go from opaque, closed objects, so is a simple test to determine whether a page of the object can be seen or not to compare the direction of the normal vector of the triangle with the line of sight.

Normal of the triangle ( cross product of and ):

Check whether Normal in the viewing direction ( scalar product of and ):

Where and are oriented triangle edges and the view direction vector.

If the result, the surface can be seen ( from the front), with earnings not (or only from behind ). This requires that the surface normal at a point away from the body of the body. Is there an area visible, then go through the next steps of the graphics pipeline. If the area is not visible, it passes no further action is therefore discarded.

The back face culling should be to make the entire process as efficient as possible, be applied as early as possible. It is often the first step of a graphics pipeline.

Similarly, there is the front face culling, in which the front pages are discarded and only the back surfaces of an object to be drawn. However, this is only needed for special effects (for example, the shadow volumes).