Problem with lookAt vertex shader / model space

Hi all, I'm trying to write an unlit shader that make each "particle" (a quad I've generated with a component with random RGBA vertex colors) look at the camera. My code works if the game object is at world zero but not if the transforms are touched. There seems to be something wrong with my space conversion.

I've seen these posts:
http://answers.unity3d.com/questions/745308/-worldspacecamerapos-and-converting-to-object-spac.html
http://answers.unity3d.com/questions/282867/unity-shader-worldobject-matrix-1.html

But nothing is working for me. Plus they are for Unity 4.

This is my thought process:
1. Each quad is 1 x 1 units in size and centered at local zero. This all works fine.
2. All the vertices of the same quad are given the same random colors in RGBA vertex color. This all works fine.
3. Get the world space center of the quad
4. Get a vector between world space center of the quad and the world space camera position
5. Create and apply a lookAt matrix.
6. Offset the quads position in local space.
7 Apply MVP matrix.

Code (CSharp):

1. v2f vert (appdata v)
2.             {
3.                 v2f o;
4.  
5.                 float4 localSpaceVert = v.vertex;
6.                 float4 debiasedColor = (v.color  * 2.0) - 1.0;  // v.color = float4(randomNumber(0-1), randomNumber(0-1), randomNumber(0-1), randomNumber(0-1))
7.  
8.                 // Local space particle position
9.                 float3 localSpaceParticlePos = debiasedColor * _ParticleBounds; // default = float3(1,1,1)
10.                
11.                 // Get world space position of particle
12.                 float3 worldSpaceParticlePos = mul(_Object2World, localSpaceParticlePos);
13.  
14.                 // Get particle - camera vector
15.                 float3 camVect = normalize(worldSpaceParticlePos - _WorldSpaceCameraPos);
16.                
17.                 float3 up = float3(0, 1, 0);
18.  
19.                 // Create LookAt matrix
20.                 float3 zaxis = camVect;
21.                 float3 xaxis = normalize(cross(up, zaxis));
22.                 float3 yaxis = cross(zaxis, xaxis);
23.  
24.                 float4x4 lookatMatrix = {
25.                     xaxis.x,            yaxis.x,            zaxis.x,       0,
26.                     xaxis.y,            yaxis.y,            zaxis.y,       0,
27.                     xaxis.z,            yaxis.z,            zaxis.z,       0,
28.                     0, 0, 0,  1
29.                 };
30.  
31.                 // Apply LookAt matrix
32.                 localSpaceVert = mul(lookatMatrix, localSpaceVert);
33.  
34.                 // Apply local particle position offset
35.                 localSpaceVert.xyz += localSpaceParticlePos.xyz;
36.  
37.  
38.                 // Apply MVP matrix to model
39.                 o.vertex = mul(UNITY_MATRIX_MVP, localSpaceVert);
40.                
41.                 o.uv = v.uv;              
42.                 o.color = v.color;
43.  
44.                 return o;
45.             }

Any help would be greatly appreciated

TNKS!

G

 

Welp, as usual explaining this on the forum made me think of the answer. I needed to do everything in local space and I also needed to make sure _WorldSpaceCameraPos is a float4 with w = 1.

Code (CSharp):

1. v2f vert (appdata v)
2.             {
3.                 v2f o;
4.  
5.                 float4 localSpaceVert = v.vertex;
6.                 float4 debiasedColor = (v.color  * 2.0) - 1.0;  // v.color = float4(randomNumber(0-1), randomNumber(0-1), randomNumber(0-1), randomNumber(0-1))
7.  
8.                 // Local space particle position
9.                 float4 localSpaceParticlePos = debiasedColor * _ParticleBounds; // default = float3(1,1,1)
10.                 localSpaceParticlePos.w = 1;
11.                                
12.                 // Get camera pos in local space
13.                 float3 localSpaceCameraPos = mul(_World2Object, float4(_WorldSpaceCameraPos.xyz, 1));
14.                
15.                 // Get particle - camera vector
16.                 float3 camVect = normalize(localSpaceParticlePos - localSpaceCameraPos);
17.                
18.                 float3 up = float3(0, 1, 0);
19.  
20.                 // Create LookAt matrix
21.                 float3 zaxis = camVect;
22.                 float3 xaxis = normalize(cross(up, zaxis));
23.                 float3 yaxis = cross(zaxis, xaxis);
24.  
25.                 float4x4 lookatMatrix = {
26.                     xaxis.x,            yaxis.x,            zaxis.x,       0,
27.                     xaxis.y,            yaxis.y,            zaxis.y,       0,
28.                     xaxis.z,            yaxis.z,            zaxis.z,       0,
29.                     0, 0, 0,  1
30.                 };
31.                
32.                 // Apply LookAt matrix
33.                 localSpaceVert = mul(lookatMatrix, localSpaceVert);
34.  
35.                 // Apply local particle position offset
36.                 localSpaceVert.xyz += localSpaceParticlePos.xyz;
37.  
38.                 // Apply MVP matrix to model
39.                 o.vertex = mul(UNITY_MATRIX_MVP, localSpaceVert);
40.                
41.                 o.uv = v.uv;              
42.                 o.color = v.color;
43.  
44.                 return o;
45.             }