[vtkusers] Separating actors for different render passes

[Ken Martin]

On Sun, Jul 9, 2017 at 4:33 PM, Milef, Nicholas Boris <milefn at rpi.edu>
wrote:

> 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?
>

The passes can modify a mapper's shader but a mapper does not store shaders
per pass.


> 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.
>

VTK caches and shares shaders between mappers so once a given shader
program has been used once it will be not recompiled for the duration of
the run.


> 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.
>

When you specify a render pass on the renderer, whatever render pass you
specify takes full control of the render process and the default process is
skipped.

Thanks
Ken



> ------------------------------
> *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/Ope
> nGL2/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->GetRequi
> redKeys());
>       this->NumberOfRenderedProps+=rendered;
>     }
>     ++i;
>   }
> }
>
>
>
>
> On Thu, Jul 6, 2017 at 3:30 PM, Milef, Nicholas Boris <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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>
>
> --
> Ken Martin PhD
> Distinguished Engineer
> Kitware Inc.
> 28 Corporate Drive
> Clifton Park NY 12065
>
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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065

This communication, including all attachments, contains confidential and
legally privileged information, and it is intended only for the use of the
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