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Display reversed normals?

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stu
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This might be a ridiculously simple question - how do I display/visualize reversed/flipped normals in the viewport? Displaying primitive normals doesn't provide much feedback in complex geometry, it's easy to miss stuff.

Numerous searches in the forums/documentation came up empty.
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malexander
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If they're auto-generated normals you can turn on Backface Culling (Optimization tab) and it'll remove all incorrectly wound polygons. If the normals are defined by an attribute, you'd have to write an attrib wrangle which compares the face and point/vert normal and assigns Cd = {1, 0 ,0} if dot(faceN, N) < 0.
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peteski
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Not sure if this is what you are looking for but you could turn on remove backfsces in the optimize tab of the display options (press d in the viewport in case you don't already know)
That might make it a bit easier??


http://www.sidefx.com/docs/houdini/ref/windows/displayopts_3d#optimize-tab [sidefx.com]
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stu
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Thanks - I was hoping for a “turn bright red!” button. I can turn the display for the backfaces off but it's not the shining beacon of “this is broken!” that that I was looking for. Using an attribute wrangle SOP provides no joy - what am I doing wrong?
Edited by stu - April 10, 2017 10:58:28
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stu
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As an alternative I'm trying to put together a two-sided constant shader (which I'm also having trouble with) - I am REALLY rusty.
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peteski
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This is probably a bit hacky but could you do this? I don't think the two sided material shows up in the viewport.

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stu
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Yeah, that only works if the faces visible through the reversed faced are reversed as well, and the geometry that I'm dealing with is sufficiently complex that making the offenders invisible won't be immediately obvious.
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peteski
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Oh no, sounds like you are dealing with a pretty broken mesh I wonder if there's something that could rebuild that for you…
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tamte
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create camera
group backfacing from that camera
color prims in backfacing group
then navigate viewport locked to that camera (to make sure camera updates with navigation)

example:

Attachments:
color_backfacing.hip (244.4 KB)

Tomas Slancik
FX Supervisor
Method Studios, NY
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stu
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Thanks I'll try it out.
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tas3d
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twod
If they're auto-generated normals you can turn on Backface Culling (Optimization tab) and it'll remove all incorrectly wound polygons. If the normals are defined by an attribute, you'd have to write an attrib wrangle which compares the face and point/vert normal and assigns Cd = {1, 0 ,0} if dot(faceN, N) < 0.

would you mind elaborating or making an example how to do this?

Im not sure if I got ur method right.

Thanks

Attachments:
backface.hip (67.7 KB)
backface.JPG (41.3 KB)

Michal Tas Maciejewski @ www.vfxtricks.com
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