Timeline for check whether `trace()` collide a face at back or front side?
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
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| Jul 3, 2020 at 0:55 | vote | accept | cppBeginner | ||
| Jul 2, 2020 at 17:02 | answer | added | Robin Betts♦ | timeline score: 2 | |
| Jul 2, 2020 at 8:56 | comment | added | cppBeginner |
@Robin :: Nice example. Thanks. You can post answer if you want. I don't plan to do. I am too satisfied for now. If you didn't say about dPdu, I couldn't reach this point of knowledge. Your original question is really good too.
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| Jul 2, 2020 at 8:50 | comment | added | Robin Betts♦ | Fantastic. Example here | |
| Jul 2, 2020 at 7:18 | comment | added | cppBeginner |
@Robin Here is the nutshell : point ps[3]; getmessage("trace","geom:trianglevertices",ps); vector trueNormal= cross(ps[1]-ps[0],ps[2]-ps[0]); I need to test more.
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| Jul 2, 2020 at 5:47 | comment | added | cppBeginner | @Robin I can use clockwise/counter-clockwise check (cross-product). In my simple test, it works. Thanks. | |
| Jul 2, 2020 at 1:43 | comment | added | cppBeginner | @Robin :: Thank. It gives me some idea. Perhaps "geom:trianglevertices" might be useful. I am investigating. docs.blender.org/manual/en/2.79/render/cycles/nodes/osl.html ... yea, look like it works. | |
| Jul 1, 2020 at 18:15 | comment | added | Robin Betts♦ |
I'm stumped. The information we need is backfacing, as determined by the clockwise / anticlockwise order of vertices around the polygon containing the shading point, from the ray's POV. The only way I can find of accessing this information is via the backfacing() function, but that can only be called on the shaded P, not on a P we hit ourselves, with a probing ray. I've tried vertex locations, dPdu,dPdv.. .... all sorts.
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| Jul 1, 2020 at 11:59 | history | edited | cppBeginner | CC BY-SA 4.0 |
added 228 characters in body
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| Jul 1, 2020 at 10:16 | history | edited | cppBeginner | CC BY-SA 4.0 |
added 5 characters in body
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| Jul 1, 2020 at 10:10 | history | asked | cppBeginner | CC BY-SA 4.0 |