SHADER: Get object position or distinct value per object

Question

Is it possible to get the current Object's 'base' world position in a vertex function?

I was thinking something like this:

float3 baseWorldPos = mul ( _Object2World, float4(0,0,0,0) ).xyz;

...but on testing I'm fairly certain it's returning a zero vector ( because its a multiplication? ).

Otherwise is there another way to get a distinct value per object, so that a shader's effects can be made unique for each individual object?

Thanks.

Answer 1

Best Answer

Answer by mig · Mar 26, 2012 at 02:57 PM

To get the position, you need to transform float4(0,0,0,1).

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Pawl · Jun 21, 2014 at 08:04 PM 0

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I just came here to say this works great, thanks!

Brenden-Frank · Oct 26, 2015 at 07:28 PM 0

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Am I missing something here? None of this appears to work (Unity 5.2 Deferred Rendering) float timeOffset = length(mul(_Object2World, float4(0,0,0,1)));

Answer 2

Answer by tonyoakden2 · Oct 23, 2017 at 04:21 AM

I think the position is in the last row of the matrix and you can use the HLSL swizzle command to get it directly thus:

float3 baseWorldPos = unity_ObjectToWorld._m30_m31_m32;

Having said that it's quite possible the shader compiler optimizes the whatever the code anyway.

also it might be ObjectToWorld._m03_m13_m23; :)

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defrummel · Aug 27, 2020 at 04:03 PM 0

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Its ObjectToWorld._m03_m13_m23

Answer 3

Answer by defrummel · Aug 27, 2020 at 04:04 PM

float3 baseWorldPos = unity_ObjectToWorld._m03_m13_m23;

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Answer 4

Answer by JLJac · Oct 19, 2020 at 08:08 AM

Hi, I'm trying to do this with deferred rendering and have a surprising issue - at certain camera angles the world pos (unity_ObjectToWorld._m03_m13_m_23) jumps to (0,0,0).

This confuses me, because to my understanding ObjectToWorld should be independent of the camera? I don't get why the transformation between object and world space would be affected by the projection matrix at all, to my understanding they should be completely separate.

The issue is not there in forward rendering mode.

If anyone with more insight could help explain that would be much appreciated!

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sarahnorthway · Jul 19, 2021 at 05:05 AM 2

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Batching! As soon as 2+ objects are batched, unity_ObjectToWorld._m03_m13_m_23 becomes 0,0,0 (rather than say a point between the batched objects). Moving the camera can change the batches.

JLJac sarahnorthway · Jul 19, 2021 at 07:33 AM 0

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Yeaah that makes a lot of sense! Thank you!

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