[PyOpenGL-Users] Need help about Picking

[Marco A. <mar...@ex...>]

Hi, I followed a lot of tutorials about picking and I decided to use the
Selection Buffer.

 

Now, the code that I wrote works as attended but I am in trouble to discover
"the nearest object". 

 

In fact, I wrote in my code(as I successfully learned at
http://pyopengl.sourceforge.net/documentation/opengl_diffs.html) :

.

hits = glRenderMode(GL_RENDER)

for record in hits:

min_depth, max_depth, names = record

.

 

and I tried to obtain the lower value of "min_depth" (= "the nearest
object") but the result is no correct: the reason is that all my returned
values of min_depth are identical. 

 

Probably it is perhaps caused by a truncated internal representation - I am
not sure, I am a novice in python too -, or by a bad pyopengl configuration.

 

For example, at page
http://www.dei.isep.ipp.pt/~matos/cg/docs/manual/gluPerspective.3G.html I
read:

 

"roughly log2r bits of depth buffer precision are lost. Because r approaches
infinity as zNear approaches 0, zNear must never be set to 0."

 

and I used "gluPerspective(45, 1.0*width/height, 0.05, 100.0)" with the
value "0.05" near to 0.  I tried to change "0.05" in "1.0" but I obtain the
bad effect that my model disappear soon when I zoom into ).

 

Can you suggest me the correct way to calculate the lower value of
"min_depth"? Or can you suggest me a alternative method to simulate a pick?
I'd like to avoid color based method.

 

Thank you for your help.

 

Marco Avellino