Courses
Sections
Projects
Wiki
News
Forums
Surveys
Mailing Lists| Author | Message |
|---|---|
|
skim144
Posts: 63
|
Posted 12:01 Jun 07, 2015 |
1. For storing pseudo depth information, why doesn't opengl implement use conversion equation like this?
(Pz - N)/(F-N) = (z*+1)/2
2. How are equations z* = (a*Pz + b)/(-Pz) , a value, and b value derived?
|
|
lmann2
Posts: 156
|
Posted 17:16 Jun 07, 2015 |
a = -(F+N) / (F-N) b = (-2FN/F-N) pg350 "we choose them so that the pseudodepth varies between -1 and 1" pesudodepth produces *z the depth of point P that we need because projection discards depth information that we need for things like clipping. I don't know if that answered your question, but I hope it helps. |
|
skim144
Posts: 63
|
Posted 17:38 Jun 07, 2015 |
Thanks Laura, i was actually asking how these values
a = -(F+N) / (F-N)
b = (-2FN/F-N)
Were derived. If i learn how to derive it, it would help me remeber it. But nowhere in the book i could find the derivation.
Last edited by skim144 at
17:39 Jun 07, 2015.
|
|
lmann2
Posts: 156
|
Posted 18:03 Jun 07, 2015 |
That's what I thought, but I wasn't sure. The book just mentions that the choice is arbitrary, but "we find out later why that's a good choice", lol. I think the choice has something to do the preserving depth along the z-axis. Also, I agree, being able to derive all the equations in this class would solve everything memorizing is a waste of time.
|
|
eykang
Posts: 95
|
Posted 10:11 Jun 08, 2015 |
It is a simple derivation. Given z* = (a*Pz + b)/(-Pz), to calculate a and b, use Pz=-N when z*=-1 and Pz=-F when z*=1. The given equation expresses the inverse relationship of z* and Pz. Last edited by eykang at
10:56 Jun 08, 2015.
|
|
skim144
Posts: 63
|
Posted 10:38 Jun 08, 2015 |
got it. Thanks! Last edited by skim144 at
11:00 Jun 08, 2015.
|
