Shadergraph: How do I get an object's rotation value inside of shadergraph? (HDRP)

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Hello, I'm trying to add a rotational value to the "Rotate About Axis" node to offset my vertices positions relative to the object. I need to use the object's rotation.euler.y value to dynamically offset those vertices, but I can't seem to find a way to reference the object's rotation value inside of shadergraph? Right now I just have a float "Counter Rotation" in place of the rotation for testing purposes, but I need the shader to be able to dynamically plug in the object's y rotation value to compute the vertex positions.

Please help, thank you!

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Answer by andrew-lukasik · May 23, 2021 at 10:41 AM

Try multiplying {1,0,0} vector by InverseModel matrix and then plug resulting x and z components into atan2

shader graph inverse rotation euler angle y

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Babyarm · May 23, 2021 at 06:26 PM 1

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omg that worked perfectly! thank you so much! I was stuck on this part for so long and you just made my entire week!

Question: what exactly is the inverse model matrix, and would you $$anonymous$$d explaining what the math behind this formula is? I couldn't find too much documentation on what exactly the transformation matrix does but I'd love to learn more about it.

Thanks in advance!

andrew-lukasik Babyarm · May 24, 2021 at 07:58 AM 0

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what exactly is the inverse model matrix

Afaik Model matrix is more or less a transform.localToWorldMatrix and Inverse Model is just transform.localToWorldMatrix.inverse. So, role of this matrix is tell shader how every vertex of your mesh (or source file "model", as it was called 20 years ago) should be transformed to display it as rotated, scaled and positioned correctly in space. I proposed inverse matrix here only because you wanted to negate (or "inverse") the rotation.

math behind this formula

There is not that much to it, really. Atan2 is there to measure that angle in XZ plane. And because of how atan2 function works (angle 0 is {1,0} as input vector) I made sure to feed it the correctly oriented vector by multiplying {1,0,0} with this matrix (multiplication will rotate it and this rotation we want to measure here).

Babyarm andrew-lukasik · May 24, 2021 at 08:21 PM 0

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Awesome! That makes a lot of sense. Thanks for the explanation, I learned a lot!

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kbkmn · Sep 24, 2021 at 04:10 PM 0

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Im trying to solve similar problem, but this method gives me rotation relative to 0,0,0. How do you get local rotation in shader graph? alt text

screenshot-2021-09-24-at-190438.png (148.5 kB)

andrew-lukasik kbkmn · Sep 25, 2021 at 04:23 PM 0

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Shader has no access to scene hierarchy data by default. If you want to change that you must pass this data manually via material property block.

kbkmn andrew-lukasik · Sep 26, 2021 at 09:09 PM 1

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I solved the issue by setting position column to zero in transformation matrix alt text

screenshot-2021-09-27-at-000804.png (61.6 kB)

screenshot-2021-09-27-at-000848.png (319.7 kB)

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nicmarxp · Dec 15, 2021 at 08:06 AM 0

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Amazing, this worked! I used this in 2D and had to change the split node B->B to use G->B instead, to make it work when rotating in Z. Also I had to change from Inverse Model to Model on the first node. Thank you!

andrew-lukasik nicmarxp · Dec 15, 2021 at 10:43 AM 0

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Hi. Ask this question as a separate thread, explain the situation, link here and we will figure it out.

nicmarxp andrew-lukasik · Dec 15, 2021 at 01:27 PM 0

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Thanks, i have no more questions. You might have seen my previous comment, but that was a mistake. :)

Shadergraph: How do I get an object's rotation value inside of shadergraph? (HDRP)

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