matcap render support

samwit · May 13, 2025, 12:35pm

Hi vtk helpers,

Now I’m using vtk9.3. Does it support MatCap render? Or is there any alternative I can resort to?

Thx a lot,
Samuel

mwestphal · May 13, 2025, 12:40pm

VTK does not support matcap but F3D implements a version of it using VTK:

github.com/f3d-app/f3d

vtkext/private/module/vtkF3DPolyDataMapper.cxx

master


      
            std::map<vtkShader::Type, vtkShader*> shaders, vtkRenderer* ren, vtkActor* actor)
          {
            if (this->RenderWithMatCap(actor))
            {
              auto fragmentShader = shaders[vtkShader::Fragment];
              auto FSSource = fragmentShader->GetSource();
          
              std::string customLight = "//VTK::Color::Impl\n"
                                        "vec2 uv = vec2(normalVCVSOutput.xy) * 0.5 + vec2(0.5,0.5);\n"
                                        "vec3 diffuseColor = vec3(0.0);\n"
                                        "vec3 ambientColor = texture(matcap, uv).rgb;\n";
          
              vtkShaderProgram::Substitute(FSSource, "//VTK::Color::Impl", customLight);
              fragmentShader->SetSource(FSSource);
            }
            else
            {
              this->Superclass::ReplaceShaderColor(shaders, ren, actor);
            }
          }

You can either implement it yourself using a similar shader or use F3D directly is that fits what you want to do.

samwit · May 14, 2025, 9:11am

Hi Mathieu,

I’ve tried out the way how to drive the code and it seems to work well.

Thanks very much for your help!

samwit · May 14, 2025, 10:06am

Hi Mathieu,

Sorry that I have one more question about the code below:

It seems to be a hotfix to the default shader impl which is very useful.
Is there any user-guide about how to write code like that?

mwestphal · May 20, 2025, 8:28am

This is not well documented, you can find this old wiki article: Shaders In VTK - KitwarePublic