Question 5124 – UGC NET CS 2018 JUNE Paper-2
December 1, 2023Question 5126 – UGC NET CS 2018 JUNE Paper-2
December 1, 2023Question 5125 – UGC NET CS 2018 JUNE Paper-2
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 onto the screen starting with the most nearest polygon.
S2 : Backface Culling refers to eliminating geometry with back facing normals.
Correct Answer: B
1. Painter’s algorithm
-A depth sorting method
-Surfaces are sorted in the order of decreasing depth
-Surfaces are drawn in the sorted order, and overwrite the pixels in the frame buffer
-Subtle difference from depth buffer approach: entire face drawn
-Two problems:
1. It can be nontrivial to sort the surfaces
2. There can be no solution for the sorting order
2. Back Face Culling
-Back faces: faces of opaque object which are “pointing away” from viewer
-Back face culling – remove back faces (supported by OpenGL)
How to detect back faces
-If we find backface, do not draw, save rendering resources
-There must be other forward face(s) closer to eye
-F is face of object we want to test if backface
-P is a point on F
-Form view vector, V as (eye – P)
-N is normal to face F
3. View-Frustum Culling
-Remove objects that are outside the viewing frustum
-Done by 3D clipping algorithm (e.g. Liang-Barsky)
4. Ray Tracing
-Ray tracing is another example of image space method
-Ray tracing: Cast a ray from eye through each pixel to the world.
5. Z(Depth buffer algorithm)