UGC NET JULY 2018 (Computer Science And Applications Paper-II) (Question 9)

UGC NET JULY 2018 (Computer Science And Applications Paper-II) (Question 9) 

 Q9. Which of the following statements is/are True regarding the solution to the visibility problem in 3D graphics ?

S1 : The Painter's algorithm sorts polygons by depth  and then paints (scan - converts) each polygon on to the screen starting with the most nearest polygon.

S2 : Backface Culling refers to eliminating geometry with backfacing normals.

Code: 

(1). S1 only                                                                   (2). S2 only

(3). Both S1 and S2                                                      (4). Neither S1 nor S2 

Answer : (2) S2 only

Reason :

For S1 Statement :

The painter's algorithm, also known as a priority fill, is one of the simplest solutions to the visibility problem in 3D computer graphics. The name "painter's algorithm" refers to the technique employed by many painters for painting distant parts of a scene before parts which are nearer thereby covering some areas of distant parts. The painter's algorithm sorts all the polygons in a scene by their depth and then paints them in this order, farthest to closest. It will paint over the parts that are normally not visible which solving the visibility problem at the cost of having painted invisible areas of distant objects. 

So according to above paragraph the option S1 is FALSE.

For S2 Statement :

Backface culling is an important part of how a 3D engine performs visibility checks. Its purpose is to detect polygons that are invisible in a particular scene that is, polygons that face away from the viewer. The process is similar to clipping, which determines if polygons are within the camera's field of view at all, and if not, are not rendered.

Back-face culling is a method in computer graphics programming which determines whether a polygon of a graphical object is visible; if it is not, the polygon is "culled" from rendering process, which increases efficiency by reducing the number of polygons that the hardware has to draw.
The vertices of front-facing polygons wind in a clockwise fashion, so polygons that face away from the camera are in a counter-clockwise order relative to the current view. When back-faces are culled, these polygons are not drawn. 

So according to above paragraph the option S2 is TRUE.