Resolved Question about mesh Tangent data

I'm curious if tangent data for deforming meshes can be stored in any way. I was trying to calculate tangents in Blender's Geometry Nodes (mostly failing miserably), and came to conclusion they have to be recalculated every frame based on vertex position changes

 

I don't understand the question. Tangents for normal mapping are stored like normals as vertex attributes in object space. During skinned rendering tangent vectors are transformed just like normals.

 

Okay, I got you. So skinning transformation is applied not only to points, but to tangents and normal vectors. For some reason, Blender doesnt expose tangent data in its Geometry Nodes, and it warped my understanding of the topic. (I am asking those questions because I hope to recreate my geonode tools in Unity one day)

 

Yes, you can download the built-in shaders to see how it is done. This is from Internal-Skinning.compute:

Code (CSharp):

1.     MeshVertex ouputVertex;
2.  
3.     ouputVertex.pos = mul(blendedMatrix, float4(vPos, 1)).xyz;
4.  
5. #if SKIN_NORM
6.     ouputVertex.norm = mul(blendedMatrix, float4(vNorm, 0)).xyz;
7. #endif
8.  
9. #if SKIN_TANG
10.     ouputVertex.tang.xyz = mul(blendedMatrix, float4(vTang, 0)).xyz;
11.     ouputVertex.tang.w = vert.tang.w;
12. #endif
13.  
14.     StoreVert(outVertices, ouputVertex, t);

It only needs a normal and a tangent. The bitangent (aka binormal) is calculated on the fly, it seems.

By the way, the typo in ou(t)putVertex is not mine

Unfortunately, I know very little about Blender, so can't help you with that.

 

I see, understandable enough. I have another question. It seems that shader code in Unity supports matrices. Can we pass some custom matrix into surface shader directly (like, as there is input format for color, so there is for matrix), or it have to be reconstructed inside a shader from separate position, rotation and scale vectors?

 

Yes, but it depends how you want to pass it.

There is no shader property for matrices, so you can only pass it in code. However, you can always pass it as 3 or 4 vectors that you reassemble in the shader.

https://docs.unity3d.com/ScriptReference/Shader.SetGlobalMatrix.html
https://docs.unity3d.com/ScriptReference/Material.SetMatrix.html
https://docs.unity3d.com/ScriptReference/MaterialPropertyBlock.SetMatrix.html

 

Passing it from code this way works fine, thank you