Got this report by email (the sender has some problems posting here):

------------------------------
Could someone please check this scene, it looks like there is a serious bug 
(maybe a mem leak) in the "isosurface object" feature.
You will see an isosurface DISAPPEAR after a certain number of pixels has 
been rendered successfully. This shows up only at resolutions like 
1024x768, not in small previews.

dAWiDi, pov### [at] xxs-swpde


// POVRAY 3.5 beta 4 bug report "ISOSURFACE DISAPPEARS AT HIGH RESOLUTION", 
example scene file
// I have been playing around with the new isosurface feature quite a bit, 
but now
// I think I have found a serious bug in this thing:
// When I render this scene at [1024x768 AA], the silvery isosurface object
// is totally ignored after about 30% of the render. This bug also occured
// with POVRAY 3.5 beta 1. It seems it can be avoided by going to extremely 
high
// max_gradient (let's say 50) and accuracy (below 0.0001), but the object
// actually is not as complex as to justify settings that cause the render
// to run slower than 10 PPS. By the way, the 192x144 preview and partial 
test renders of
// the 1024 resolution did not have this problem, as obviously it only kicks in
// after a certain number of pixels have been rendered.
// NOTE: If you're doing test renders to see the error, you have to let it 
render the
// entire image at 1024x768, even though it will take several minutes (30 
mins on my
// Celeron 466), because otherwise it might not occur. You can render it at 
a very
// low resolution first, to see what it's supposed to look like.
// I just hope someone can fix it, since this sort of thing could occur in any
// isosurface scene.
// Even though I don't think this is system-dependent, here's my config:
// intelCeleron 466 @466MHz, 192MB, 30GB, MSWin98-1, POVRay 3.5 beta 1&4.
// dAWiDi, pov### [at] xxs-swpde
#include "colors.inc"
#include "textures.inc"
global_settings{
max_trace_level 50
adc_bailout 1/32
}
camera {location <-4,4,-5>
	angle 60
	look_at <0,-.5,0>
	}
light_source {<-15,100,5> color White*.7}
light_source {<-15,35,-40> color rgb <0,85/255,155/255> shadowless}
light_source {<15,30,-40> color rgb 1-<0,85/255,155/255> shadowless}

#declare xxsStdSky=sky_sphere{
	pigment{gradient y color_map{[0 White][1 rgb<.5,.5,1>]}}
	pigment{bozo scale .5 rotate x*90 turbulence 1 color_map{[.05 color 
Gray95][.2 color Clear]} scale<1,.6,1>}
	pigment{bozo scale .07 turbulence .7 color_map{[0 color White][.3 color 
Clear]} scale<5,.6,1> }
	}
sky_sphere{xxsStdSky}
fog{fog_type 2 distance 1000/5 fog_offset 10 fog_alt 20 color 
rgb<0,85/255,155/255>}
background{color rgb .25}

#declare testfunki=function{pattern{crackle}}

object{isosurface{
#declare pattskali=3;
#declare Blob_threshold=0.1;
#declare Funki1=function{ y-1*(sin(x)*cos(z*x/5))}
#declare Funki2=function{ 
sqrt(x^2+(y-.6)^2+z^2)-1.5-.2*testfunki(x*pattskali,y*pattskali,z*pattskali)}
function{(1+Blob_threshold)-Blob_threshold^Funki1(x,y,z)-Blob_threshold^Funki2(x,y,z)}
contained_by{box{<-5,-1.01,-6>, <18,3,20>}}
max_gradient 5
threshold 0
accuracy 0.0005
}
texture{Silver_Metal}
}

//End Of File


-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

Post a reply to this message

Warp schrieb in Nachricht <3bb0b351@news.povray.org>...

>// I think I have found a serious bug in this thing:
>// When I render this scene at [1024x768 AA], the silvery isosurface object
>// is totally ignored after about 30% of the render. This bug also occured
>// with POVRAY 3.5 beta 1.

I get the blue background-fog already at approx. 60% of a 640x480 render.

PII 450, Win98, 128 MB, Pov 3.5 beta 4

I rendered with some additional programs running.

Marc-Hendrik

Post a reply to this message

>>// I think I have found a serious bug in this thing:
>>// When I render this scene at [1024x768 AA], the silvery
isosurface object
>>// is totally ignored after about 30% of the render. This bug
also occured
>>// with POVRAY 3.5 beta 1.
>
>I get the blue background-fog already at approx. 60% of a
640x480 render.
>
>PII 450, Win98, 128 MB, Pov 3.5 beta 4
>

That's odd: A second render at 1024x768 was quite fine, just two
artefacts (fog colour) in the middle of the pic. I did not close
Pov between those two renders, but I made some tests without the
Iso. For me it looks like a max_gradient problem (no bug) now,
but what do I know about it?

Marc-Hendrik

Post a reply to this message

In article <3bb0de46@news.povray.org> , "Marc-Hendrik Bremer" 
<Mar### [at] t-onlinede> wrote:

> That's odd: A second render at 1024x768 was quite fine, just two
> artefacts (fog colour) in the middle of the pic. I did not close
> Pov between those two renders, but I made some tests without the
> Iso. For me it looks like a max_gradient problem (no bug) now,
> but what do I know about it?

Try it with "evaluate"?


    Thorsten

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Thorsten Froehlich schrieb in Nachricht <3bb0dffd@news.povray.org>...
>Try it with "evaluate"?


It reports something around 95.7 which is probably not too high with a
crackle-function in the Iso. But that max_gradient of 5 is too low in this
case. I don't know why dAWiDi thinks that the object is not complex enough
to go under 10 PPS.

Marc-Hendrik

Post a reply to this message

In article <3bb0e726@news.povray.org> , "Marc-Hendrik Bremer" 
<Mar### [at] t-onlinede> wrote:

> It reports something around 95.7 which is probably not too high with a
> crackle-function in the Iso. But that max_gradient of 5 is too low in this
> case. I don't know why dAWiDi thinks that the object is not complex enough
> to go under 10 PPS.

No, 95 sounds good for crackle.  So in summary the problem reported by
"dAWiDi" <pov### [at] xxs-swpde> is a user error.  The suggested solution is
to use an appropriate max_gradient and to read the documentation.

Thanks for finding the problem Marc-Hendrik!

---

As this is not the first time someone reports this "bug" and turns out to be
nothing more than a too low max_gradient, I think this really needs a FAQ
entry in the documentation.  Warp, do you think you could write and add such
a FAQ entry, please?

    Thorsten

____________________________________________________
Thorsten Froehlich
e-mail: mac### [at] povrayorg

I am a member of the POV-Ray Team.
Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message

Thorsten Froehlich <tho### [at] trfde> wrote:
: Warp, do you think you could write and add such a FAQ entry, please?

  Of course I could.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

Post a reply to this message

Wasn't it Thorsten Froehlich who wrote:
>In article <3bb0e726@news.povray.org> , "Marc-Hendrik Bremer" 
><Mar### [at] t-onlinede> wrote:
>
>> It reports something around 95.7 which is probably not too high with a
>> crackle-function in the Iso. But that max_gradient of 5 is too low in this
>> case. I don't know why dAWiDi thinks that the object is not complex enough
>> to go under 10 PPS.
>
>No, 95 sounds good for crackle.  So in summary the problem reported by
>"dAWiDi" <pov### [at] xxs-swpde> is a user error.  The suggested solution is
>to use an appropriate max_gradient and to read the documentation.

The symptoms don't sound anything remotely like the effects that
normally occur with an insufficient max_gradient.

There are max_gradient artefacts in the scene (tiny black holes near the
tips of the crackly bit) but they don't change significantly when the
render size is changed, and they certainly don't change at all between
the rendering of a partial scene and rendering the full scene.

I haven't yet tried rendering the full scene at 1024x768 AA, but I did
try ripping out some of the go-slow features of the scene to see if the
problem could be reproduced without the fog, the complicated sky pigment
and the reflective texture on the isosurface. The expected max_gradient
artefacts were visible, but nothing like the reported problem occurred.

The fact that changing max_gradient happens to fix it may well be
coincidental, in the same way that removing the sky, fog and reflection
happen to fix it.

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message

In article <3bb11b6d@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

> : Warp, do you think you could write and add such a FAQ entry, please?
>
>   Of course I could.

Will you?


____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message

In article <e0Z### [at] econymdemoncouk> , Mike Williams 
<mik### [at] nospamplease>  wrote:

> The symptoms don't sound anything remotely like the effects that
> normally occur with an insufficient max_gradient.

There is nothing else in the intersection code that could cause this find of
effect only appear after a specific output size as the code could not care
less of the output size.  And the original user's guess that it is a "memory
leak" is plain nonsense because those don't have this kind effect.

However, max_gradient can have this kind effect on certain patterns, so it
is max_gradient, really!

    Thorsten


____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

Post a reply to this message