_Object2World or UNITY_MATRIX_IT_MV?

In unity's vertex shader，I need transform v.normal to world space, but I don't understand _Object2World and UNITY_MATRIX_IT_MV. Which one should I use?
mul( (float3x3)_Object2World, v.normal) or mul( (float3x3)UNITY_MATRIX_IT_MV, v.normal ) ?

 

That means that I should use _Object2World for rotating v.normal from objectspace into worldspace?

 

I think you wanted to say : UNITY_MATRIX_IT_MV is for rotating normals from eye into object space.
Inverse Transpose matrix.

To sbin3776 : Yes, use _Object2World, the name is quite explicit

 

To transform normals from object to world space, use _World2Object but multiply it from the right hand side to the vector (this makes sure that you multiply the vector with the transposed matrix). (The "IT" in "UNITY_MATRIX_IT_MV" stands for Inverse Transpose" which is what you need for the correct transformation of normal vectors.)

If you are sure that your model matrix is orthogonal (no scaling), you can also use _Object2World (from the left hand side).

 

What is incorrect?

 

thanks for your answer
but
How can I know the model matrix is orthogonal ?
if it is not orthogonal ,Should I use _World2Object buy multiply it from the right hand side to the normal vector ?
Which of the following is correct:
1 mul( (float3x3) _Object2World ,v.normal ) ; //model matrix is orthogonal
2 mul ( v.normal, (float3x3) _World2Object ) ;// model matrix is not orthogonal
3 mul ( v.normal, (float3x3) transpose( _World2Object) ) ;// model matrix is not orthogonal
4 mul ( (float3x3) transpose( _World2Object) , v.normal ) ;// model matrix is not orthogonal
-------------------------------------------------------------
I think 3 is incorrect and 2==4

 

Related question
how do I grab the matrix in GLSL from the setMatrix() over in javaScript

steve

 

You think correctly.

A 3x3 matrix is orthogonal if all row vectors (or all column vectors) are of unit length and the dot product of any two row vectors (or column vectors) is 0.

 

You define a uniform matrix outside of main():

uniform mat4 mymatrix;

You can set the variable mymatrix with setMatrix() (even though you cannot define a property).

 

Isn't that the definition of orthonormal matrices ?
In orthogonal matrices, only all the row vector (or all the column vectors) are perpendicular to each other.

 

Is it possible to rotate the normals into eye space specifying the camera position manually, ignoring the current camera position?

 

Hey guys, if you're making an endless runner moving along the z axis and you need to use a projection matrix that is relative to the camera but is not affected by rotation, then just subtract the camera world position z from the vPos.z, i.e.:

Code (CSharp):

1.  
2. float4 vPos = mul (_Object2World, v.vertex);
3. float zOff = (vPos.z - _WorldSpaceCameraPos.z)/_Dist;     // offset relative to camera along the z axis
4. vPos += _QOffset*zOff*zOff; //
5. v.vertex = mul (_World2Object, vPos);
6.