[vtkusers] Drawing custom image with depth buffer and a translucent plane

Tue Oct 23 14:04:57 EDT 2018

Hi Elvis and Ken,

Thanks for the help. What it seems to start to work for me, is to use layered renderers: using two renderers, and using the first for my volume and the second for the plane. Currently I’m dealing with the depth buffer definition as I couldn’t find its definition yet in VTK code, but so far, I could draw some extent of the translucent plane in front and the other back.

I think that by fixing the depth buffer definition in my code, I would be able to mimic this behavior. I will poke you again if I succeed.

Cheers,
Pato

From: Ken Martin <ken.martin at kitware.com>
Sent: Tuesday, October 23, 2018 2:41 PM
To: Elvis Stansvik <elvis.stansvik at orexplore.com>
Cc: patricio.sandana at synopsys.com; vtkusers at public.kitware.com
Subject: Re: [vtkusers] Drawing custom image with depth buffer and a translucent plane

Maybe from vtkRenderer.h

/**
   * This flag is on and the GPU supports it, depth-peel volumes along with
   * the translucent geometry. Only supported on OpenGL2 with dual-depth
   * peeling. Default is false.
   */
  vtkSetMacro(UseDepthPeelingForVolumes, bool)
  vtkGetMacro(UseDepthPeelingForVolumes, bool)
  vtkBooleanMacro(UseDepthPeelingForVolumes, bool)

On Tue, Oct 23, 2018 at 1:32 PM, Elvis Stansvik <elvis.stansvik at orexplore.com<mailto:elvis.stansvik at orexplore.com>> wrote:
I believe this is a limitation of VTK. Translucent polygonal geometry with opacity != 1.0 can't be rendered intersected with a volume other than in a back-to-front or front-to-back manner.

Someone correct me if I'm wrong (we'd also very much like to be able to do this).

Elvis

Den fre 12 okt. 2018 kl 22:20 skrev Pato Sandana <patricio.sandana at synopsys.com<mailto:patricio.sandana at synopsys.com>>:
Hi Everyone,

I’m trying to draw a vtkVolume and a vtkPlaneWidget both intersecting and the vtkPlaneWidget is translucent. I cannot achieve that, either the plane is totally behind or front.

For a vtkActor with the same box extent this works.

I tried to get the z-buffer from the context using vtkRenderer::GetZbufferData() method, but I only get 1s. (Is this correct?)
I also tried to write the z-buffer data I got with vtkRenderer::SetZbuferData() method, but the plane is still behind.

Any hints how to achieve this? Thanks in advance.

Regards,

Pato Sandaña
TCAD Senior R&D Engineer
Synopsys Inc. – Santiago, Chile

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