UGC NET Computer Science July 2018 - II | Question 9

Question 9

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9. 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. (1) S₁ only
2. (2) S₂ only
3. (3) Both S₁ and S₂
4. (4) Neither S₁ nor S₂

Answer : (2) S₂ only

• Statement S₁ is False.
  The ‘painter's algorithm’ arranges all the polygons in a view by their depth and then paints them in this order, extreme to closest. It will paint over the existing parts that are usually not visible hence solving the visibility issue at the cost of having painted invisible areas of distant objects.
• Statement S₂ is True
  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. Detecting back-facing polygons allows us to eliminate them from an engine's rendering pipeline at an early stage, thus reducing the amount of computation and memory traffic. There are various ways to detect whether a polygon faces towards or away from the viewer, and each method has its own level of complexity and accuracy.

Statement S2 only true statement.

So, Option (2) is correct answer.

Reference : Painter’s Algorithm

Reference 1 : Painter’s Algorithm

Reference 2 : A Compact Method for Backface Culling

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