SHADER: Get *object* position or distinct value per *object*

Questions & Answers
1

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.

2

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

4

float3 baseWorldPos = unity_ObjectToWorld._m03_m13_m23;

3

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; :slight_smile:

5

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!