[vtkusers] Shader input attribute

[Nil Goyette]

Hi all, I have been seaching in the last hours how to fill an 
"attribute" variable in GLSL. There's a test TestGLSL.cxx that shows how 
to use a vertex and fragment shader, but they don't use any input 
variable. My vertex shader is:
shader->SetSourceCode(R"VertexShader(
     #version 120
     attribute vec3 next_point;
     varying vec3 vColor;

     void main() {
         float r = gl_Vertex.x - next_point.x;
         float g = gl_Vertex.y - next_point.y;
         float b = gl_Vertex.z - next_point.z;

         if (r < 0.0) { r *= -1.0; }
         if (g < 0.0) { g *= -1.0; }
         if (b < 0.0) { b *= -1.0; }

         const float norm = 1.0 / sqrt(r*r + g*g + b*b);
         vColor = vec3(r * norm, g * norm, b * norm);

         gl_Position = ftransform();
     }
)VertexShader");

The goal here is, for each point, get the vector to the next point to 
calculate the color of the line between them. I can't find a way to set 
the value of "next_point". I'm pretty sure it's always filled with 0.0 
because the output image is red, blue and green on the sides.

I tried using vtkProperty::AddShaderVariable() but I never saw any 
change and the method's documentation hints about a "uniform variable" 
so it's probably not the right way.
fibersActor->GetProperty()->AddShaderVariable("next_x", nb_points, 
next_x); // Splitted in 3 because I'm not
fibersActor->GetProperty()->AddShaderVariable("next_y", nb_points, 
next_y); // sure how to passa vtkPoints
fibersActor->GetProperty()->AddShaderVariable("next_z", nb_points, 
next_z); //object to AddShaderVariable

*tl;dr* Can you please tell me how to pass the content of a vtkPoints 
into a GLSL attribute variable? Thanks for your time.

-- 
Logo Imeka <http://imeka.ca/> 	Nil Goyette, M.Sc.
Programmer
www.imeka.ca <http://imeka.ca/>

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