Vector to eye position

OpenGL
1

Can anyone tell me how to determine a vector from a vertex to the eye/camera in the vertex or geometry shader?

Thanks!

2 
vec3 eyeVec = (gl_ModelviewMatrix * gl_Vertex).xyz;
3

Shouldn’t you put a “-” before?

4

Shouldn’t you put a “-” before?
Yeah, the question was about the opposite vector, so I guess “-” should be there.
I alsways calclate vector from eye to vertex because it’s better for reflect() and refract().

5

Thanks guys,

I’ll give it a try on monday.

I was trying this actually in the Geometry Shader. However it seems that this:

  
vec4 pos = gl_ModelViewMatrix * vertex;
gl_Position = pos;

is different from:

  
vec4 pos = vertex;
gl_Position = gl_ModelViewMatrix * pos;

Any idea why?

6

It is different. gl_Position is same but pos is different in case 1 and case 2.

7

Ok, but the actual result is different. And that is based on the gl_Position. I would expect no visual difference.

8

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