gadoid nous apporta ses lumieres en ce 2007/09/06 23:44:
> Alain <ele### [at] netscapenet> wrote:
>> gadoid nous apporta ses lumieres en ce 2007/09/06 22:23:
>>> "Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
>>>> "gadoid" <hansen at tkgate.org> wrote:
>>>> ....
>>>>
>>>> I may have narrowed the problem down for you.  It appears to be affected
>>>> ultimately by the size of the normals of the plane behind the spheres.
>>>>
>>>> Try removing the plane normal or making it smaller and see what happens.  It
>>>> doesn't matter what normal type you have on the spheres, so it's not related
>>>> to the crackle pattern.  Whatever is causing it, the normals on the plane
>>>> appear to be getting reversed by the spheres.  For example try rendering
>>>> with "bozo 4" normal on the plane and then "bozo -4" and compare.
>>>>
>>>> Hope this can help someone track down the reason or bug causing it.
>>>>
>>>> -tgq
>>> I did notice the problem only happens when the surface beyond has a normal.
>>> You are right that it may be reversing the normal, I at first thought it was
>>> just shifting it.  I'm beginning to think that this must be a POV-Ray bug,
>>> but if it is, I need to find a work-around for my scene.  I can't get rid
>>> of the "normal" on the surface behind the object, because that is water and
>>> I am using the normal to generate the waves.  I have hundreds of the
>>> "electron" objects in the scene.  The only thing I can think of is to
>>> #declare a different object for every orientation I need since the
>>> unrotated objects seem to render fine.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>> Don't rotate the texture! Instead, create the objects at the origin, rotate the
>> objects, thanslate them to the final position. As you are using spheres,
>> rotating the object or the texture will wave the same final aspect, minus the
>> normal alteration.
>>
>> In my tests, the effect depends on the axis of rotation relative to the
>> camera-object vector. An object with a z rotation just in front of the default
>> camera show no effect, while the same object shifted up/down or lateraly will
>> exibit the effect.
>>
>> --
>> Alain
>> -------------------------------------------------
>> When you don’t know what to do, walk fast and look worried.
> 
> Unfortunately, I still get the problem when I rotate the object and not the
> texture.  I was rotating the texture because in an earlier scene, I was
> using a gradient with turbulence to get rings of lightning, and I wanted
> them to have different orientations for the different instances of the
> object.  Ultimately, the sphere will have legs and thus will not be truly
> symmetrical.  I've since decided to use crackle to get lightning so I don't
> really need to rotate the texture anymore, but rotating the object still has
> the same problem.
> 
> I'm not seeing any difference in the effect irregardless of where I put the
> camera.  The unrotated sphere at <-0.5,1,0> is invisible no matter where I
> put the location and look_at.  How are you getting it to appear?
> 
> 
If you don't rotate the sphere, it's placement is irrevelent. IF you rotate the 
texture, THEN the location DOES have an effect. If the axis of rotation is 
parallel to the camera-object axis, then you don't have the problem.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you've convinced your boss that 
raytracing is really an integral part of your job title (and you really don't 
work in a position that requires it).
Quietly Watching

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