[vtkusers] What illumination formula use VTK ? (it does not look as pure Phong)

[Bill Lorensen]

If I recall, by default, uses gouraud shading as implemented in opengl:
http://en.wikipedia.org/wiki/Gouraud_shading
For very small polygons (< 1 pixel) I believe that Gouraud shading
approaches Phong Shading.

I believe you can program any illumination model you want with vtk
programmable shaders.


On Sun, Jul 29, 2012 at 9:44 AM, Jana Sefcikova <neollie at gmail.com> wrote:

> Hi, I made small algorithm when I am manually computing phong
> illumination.
> What illumination formula is used in VTK ? It looks that is not phong
> illumination.
> I would need obtain same color as VTK made is.
> ---------------------------
> I made small test :
>
> My 'phong' illumination formula is :
>    I = kd * abs((n*l)) + ks * abs(h*n) ;
> where diffuse term  kd = 0.6   and specular term ks = 0.4,
> view vector is default v = (0,0,1), light vector l is also located at
> (0,0,1),
> n is normal at the point, and h is standard halfway vector.
>
> For comparison with VTK I used same settings for drawing purely with vtk
> setting property :
> actor->GetPorperty()->SetAmbient(0);
> actor->GetProperty()->SetDiffuse(kd);
> actor->GetProperty()->SetSpecular(ks)
>
> The results are different, see attached picture.
>
> Therefore it looks that VTK is not using pure phong.  So what illumination
> formula is used in VTK ?
> It is done via shaders ? Or it is somewhere computed ?
> Where is made color computation in vtk, where those ambient, diffuse,
> specular coefficient are used ?
> I found method GetColor() in vtkProperty() , but it has different meaning,
> but i am searching for s.t. like this.
>
>
> Any hint would be highly appreciate.
> Thanks in advance.
>
>
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtkusers
>
>


-- 
Unpaid intern in BillsBasement at noware dot com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20120729/57761612/attachment.htm>