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I have a problem that never happened to me before, will explain it in a simple way :

I start a new scene, I remove the basic elements as I always do. I put a new cube + surface modifier subdivision + cast (I apply the modifiers). Then I smooth and in classic object mode no worries, I decide to take a normal map in texture mode as done a lot of times before. So I'm in material preview mode, I paint the normal map and this is where it starts when I then connect the normal map with a normal map node so that it connects correctly with the principled BSDF, still in material preview mode, all sides appear. I've tried all the possible solutions, nothing works.

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Here a pics of the new scene i tried to understand what happened.

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Here the original scene where the problem start without understanding why :

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The last pics to help you to see:

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  • $\begingroup$ Scroll down in your material settings for that material and see what Blend Mode it's using. If it's anything other than Opaque try enabling/disabling Backface Culling and/or Show Backface. $\endgroup$ Dec 18, 2022 at 0:06
  • $\begingroup$ I looked, but I hadn't touched anything here because it was really to test in a new scene. Because the problem appeared in another scene where I worked. I will show you with photo to make it more clear for you. $\endgroup$ Dec 18, 2022 at 0:16
  • $\begingroup$ Where did you get the normal texture from? There are more than one convention for normal maps, usually what differs is the green channel, it may have to be inverted. $\endgroup$ Dec 18, 2022 at 3:12
  • $\begingroup$ victorkarp.com/inverting-a-normal-map-in-blender/…. In this link he explains what I mean about the green channel, and how to fix it. $\endgroup$ Dec 18, 2022 at 3:13
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    $\begingroup$ i post the normal map i want to use here $\endgroup$ Dec 18, 2022 at 23:25

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The issue is that your normal map has a white background.

enter image description here

White means all the channels (red, green and blue) are at 1 (or 100%). So the shader is taking the geometry normals and rotating it in weird ways to get the textured normal. This is why the normals are messed up when you use this texture. The background of a normal texture for blender should be this blueish purple color:

enter image description here

(I think the RGB values are 0.5, 0.5, 1, if I'm not mistaken) The values in this color represent unchanged normals. In the places where the texture has this color, the geometry normals are unchanged. That's what you want in the background of your skull normal texture.

This probably happened because you used a png with transparent background to create the normal texture, and the background was still the default white background in photoshop. Try doing it again, but merge the skull png with the background before creating the normal map, you'll notice the background will be purple instead of white.

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