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I am having an inconsistency between outcomes using the node Geometry>Random per Island

It is the same node setup behaving differently between 2.83 and 2.9

2.83: I will get the colors assigned to the color ramp distributed within the meshes that have that material. The limitation is the “island” meaning that closed meshes will have one color assigned.

2.9: Every different face of my mesh will get a different color from the color ramp. This is not what I need since I am trying to assign random colors to multiple assets, but each asset in itself can not have a different color per face…it looks really funky

Have you experimented this?

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3 Answers 3

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not sure if answering 9 months later is going to be helpful but I came across a similar problem yesterday. In my experience Random per Island works fine until you use autosmooth (Botom Row of the picture) thats when it gets funky, it also changes if you are using hard normals (first column of the picture) or smooth normals (second column).

enter image description here

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    $\begingroup$ Hi, thanks for the post. It's completely acceptable to leave an answer to an old question, and it looks like you've provided some valuable info. $\endgroup$ May 12, 2021 at 16:31
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For me any modifier breaks the Random Per Island, I had to apply the modifiers, and now is working as expected.

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It seems that Auto Smooth splits edges when used. Random per Island assigns a random value for each connected component of the mesh, so when the edges are split, each island gets a different value and it looks like Random Per Island is broken while it works correctly.

It's the same with Harden Normals option in Bevel Modifier - it seems that it splits edges when used.

My workaround is to add WeightedNormal Modifier (but without Harden Normal option if Bevel Modifier is needed). I'm using Blender 3.4.1. by the way.

Below is an image that shows better what happens. Each row is a cube with Array Modifier and Bevel Modifier.

Random Per Island

Row 1: Just regular flat shading - Random Per Island works correctly but the beveled edges are flat shaded.

Row 2: Auto Smooth ON - Random Per Island is broken and normals are weird.

Row 3: Auto Smooth ON and Harden Normals ON - Random Per Island is broken but normals are fixed.

Row 4: Auto Smooth ON, Harden Normals ON and WeightedNormal Modifier added - Random Per Island is still broken but I'm not sure why - it seems that Harden Normals option is somehow prioritized here.

Row 5: Auto Smooth ON, Harden Normals OFF and WeightedNormal Modifier added - Random Per Island works correctly and normals are OK.

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