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Back Face culling question??

Started by PuterPaul May 10, 2004 at 5:40 AM 3 replies 900+ views

Original Post

May 10, 2004 at 5:40 AM

Hi folks, i''m in revision mode at the moment, neways for my Graphics Programming module i''m going through a past exam paper and theres one question which is confusing me. Wondering if anyone can give me a good answer. In general, back-face culling is insufficient for hidden surface removal. Show by use of an example why this is so. I''ve looked in my notes and course books but I can''t really find a good answer.

Lutz

May 10, 2004 at 5:46 AM

1) If you have two spheres, one in front of the other. If you only do back-face culling, you might still draw the front sphere before the back sphere so that the back sphere is fully visible although it is actually covered by the front sphere.

2) If two polys intersect, backface culling is insufficient.

PuterPaul

May 10, 2004 at 6:16 AM

quote:
Original post by Lutz
1) If you have two spheres, one in front of the other. If you only do back-face culling, you might still draw the front sphere before the back sphere so that the back sphere is fully visible although it is actually covered by the front sphere.

2) If two polys intersect, backface culling is insufficient.

Cool thanks, so I presume its better to use something like the Z buffer alg then??

_DarkWIng_

May 10, 2004 at 6:42 AM

quote:
Original post by PuterPaul
Cool thanks, so I presume its better to use something like the Z buffer alg then??

Use both. First a cheap BF culling, then normal Z buffer.

You should never let your fears become the boundaries of your dreams.

gamelife

May 10, 2004 at 12:29 PM

I have a related question (perhaps doesn''t deserve a new thread):

How to do BF culling just after perspective transform, i.e. in homogeneous space and _before_ clipping?

Just did a google search, but couldn''t find useful info.

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