[vtkusers] Separating actors for different render passes

[Milef, Nicholas Boris]

Thanks Ken! This is just what I was looking for. A couple of followup questions:

1. Is it possible to have an actor with different shaders for different passes? Or would we need to use separate actors/mappers since each mapper only has one shader? Recompiling shaders on the fly isn't an option for us.
2. Is it possible to replace the default vtkDefaultPass for the vtkRenderer with a different subclass of vtkDefaultPass or at least disable the default vtkDefaultPass? I couldn't find any API commands that would allow me to do this without subclassing the vtkRenderer, but I could've missed something.
________________________________
From: Ken Martin [ken.martin at kitware.com]
Sent: Thursday, July 06, 2017 4:18 PM
To: Milef, Nicholas Boris
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] Separating actors for different render passes

With the render passes you can setup as many passes as you want in whatever order you want. This shows an example where the render process is all driven by passes.

https://gitlab.kitware.com/vtk/vtk/blob/master/Rendering/OpenGL2/Testing/Cxx/TestSobelGradientMagnitudePass.cxx

As an example for shadow maps when needed we use nested opaque passes to render the scene from the view of the light sources which we then use in another opaque pass to compute lighting from the view of the camera.

Render passes also have hooks that mappers call so that passes can modify the mapper shader code etc while executing.

Passes can also use information properties on actors to filter them in other passes.  For example an outer render pass can add information on actors that causes some of them to not be rendered (or to be rendered differently) by other passes ala

// ----------------------------------------------------------------------------
// Description:
// Opaque pass with key checking.
// \pre s_exists: s!=0
void vtkDefaultPass::RenderFilteredOpaqueGeometry(const vtkRenderState *s)
{
  assert("pre: s_exists" && s!=0);

  int c=s->GetPropArrayCount();
  int i=0;
  while(i<c)
  {
    vtkProp *p=s->GetPropArray()[i];
    if(p->HasKeys(s->GetRequiredKeys()))
    {
      int rendered=
        p->RenderFilteredOpaqueGeometry(s->GetRenderer(),s->GetRequiredKeys());
      this->NumberOfRenderedProps+=rendered;
    }
    ++i;
  }
}




On Thu, Jul 6, 2017 at 3:30 PM, Milef, Nicholas Boris <milefn at rpi.edu<mailto:milefn at rpi.edu>> wrote:
Is there currently a way to separate actors into custom render passes? If I'm not mistaken, opaque objects currently get rendered before translucent objects, but is there a way to add additional geometry passes (or before opaque geometry, or between translucent and opaque geometry, etc.)?

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Distinguished Engineer
Kitware Inc.
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