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When using the 'fresnel' keyword in reflections, Linux (Redhat 7.3) and Windows (2000)
versions of POV-Ray produce different output!
This phenomenon caused a strange flickering in an animation rendered on the IMP
render-farm (which uses clients with different OS), after some experimentation I
discovered that it is caused by the fresnel reflection.
I wrote a short scene to demonstrate the effect. An image showing both outputs was
posted to p.b.images (fresnel.jpg).
For me the windows output looks "right". Any ideas what could case this effect (a bug
in the linux version?), or is something wrong with my material definition?
Is there a "workaround"?
POV-Ray for Windows: Version 3.5.icl.win32
POV-Ray for Linux: Version 3.5 Unix (.Linux.gcc)
Looking at the statiscics shows that different numbers of rays were
reflected/refracted (see below).
Ok, here's the test-scene, I've rendered it with "povray -F +D +P +H216 +W384
test.pov" on both machines.
/*-------------------------------------start----------------------------------*/
global_settings {
max_trace_level 8
}
#local glass = material {
texture {
pigment { transmit 1 }
finish {
specular 10 roughness 0.001
conserve_energy
reflection { 1 fresnel }
}
}
interior {
ior 1.5
caustics 5
fade_distance 1
fade_power 2
}
}
camera {
location <0,0,-15>
look_at <0,0,0>
up y
right x * 16/9
}
light_source {
<-100,100,-100>
color rgb 1
}
difference {
cylinder { <0,-5,0>,<0,5,0>,5.5 }
cylinder { <0,-5,0>,<0,5,0>,5 }
material { glass }
}
plane {
-z,-10
pigment { color rgb 1 }
finish { ambient 0.5 diffuse 0.5 }
}
/*-------------------------------------end----------------------------------*/
Statistics from linux version:
==============================
Statistics for test.pov, Resolution 384 x 216
----------------------------------------------------------------------------
Pixels: 82944 Samples: 82944 Smpls/Pxl: 1.00
Rays: 855752 Saved: 213640 Max Level: 8/8
----------------------------------------------------------------------------
Ray->Shape Intersection Tests Succeeded Percentage
----------------------------------------------------------------------------
Cone/Cylinder 2757604 1257284 45.59
CSG Intersection 1378802 777524 56.39
Plane 1378802 391676 28.41
----------------------------------------------------------------------------
Calls to Noise: 0 Calls to DNoise: 10
----------------------------------------------------------------------------
Shadow Ray Tests: 1515460 Succeeded: 384732
Reflected Rays: 386404
Refracted Rays: 386404
----------------------------------------------------------------------------
Smallest Alloc: 14 bytes Largest: 12296
Peak memory used: 155640 bytes
----------------------------------------------------------------------------
Time For Trace: 0 hours 0 minutes 11.0 seconds (10 seconds)
Total Time: 0 hours 0 minutes 10.0 seconds (10 seconds)
Statistics from windows version:
==============================
Statistics for F:\test\test.pov, Resolution 384 x 216
----------------------------------------------------------------------------
Pixels: 82944 Samples: 82944 Smpls/Pxl: 1.00
Rays: 917012 Saved: 223932 Max Level: 8/8
----------------------------------------------------------------------------
Ray->Shape Intersection Tests Succeeded Percentage
----------------------------------------------------------------------------
Cone/Cylinder 2972274 1354663 45.58
CSG Intersection 1486137 841641 56.63
Plane 1486137 432504 29.10
----------------------------------------------------------------------------
Calls to Noise: 0 Calls to DNoise: 10
----------------------------------------------------------------------------
Shadow Ray Tests: 1638610 Succeeded: 416873
Reflected Rays: 424768 Total Internal: 15468
Refracted Rays: 409300
----------------------------------------------------------------------------
Smallest Alloc: 25 bytes Largest: 12056
Peak memory used: 153837 bytes
----------------------------------------------------------------------------
Time For Trace: 0 hours 0 minutes 7.0 seconds (7 seconds)
Total Time: 0 hours 0 minutes 7.0 seconds (7 seconds)
----------------------------------------------------------------------------
CPU time used: kernel 0.08 seconds, user 6.87 seconds, total 6.95 seconds
Render averaged 11934.40 PPS over 82944 pixels
POV-Ray finished
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