[vtkusers] VtkUnstructuredGrid SetOpacity

[Bhanu Hariharan]

Thanks David. I have a few more questions in this regard before I make
changes to my approach.

1.  How do I tell if my graphics card supports Depth peeling. Would Depth
Peeling render it blueish green?

2. I tried vtkDepthSortPolyData but it needs vtkPolyData as input. I was
wondering if VtkUnstructuredGrid can be used for vtkDepthSortPolyData or is
there any other equivalent of vtkDepthSortPolyData for VtkUnstructuredGrid
that would render according to depth correctly.


3. If I replaced all my code and do Volume rendering, do I still need to
use vtkDepthSortPolyData?

4. I found VtkUnstructuredGrid  to be slow in rendering for large datasets
thats why I was rendering only the outer surfaces.
Is volume rendering better than VtkUnstructuredGrid  for rendering in terms
of speed.
Are there any C++ examples for Volume rendering that will help me get
started.

I really appreciate you taking the time to answer my questions.

Thanks for your help.
Bhanu





On Wed, Jan 25, 2012 at 5:26 PM, David E DeMarle
<dave.demarle at kitware.com>wrote:

>
> On Wed, Jan 25, 2012 at 5:52 PM, Bhanu Hariharan <bhanu at petrotel.com>wrote:
>
>> David, Thanks for replying.
>>
>> When I flip, I see blue AGAIN. Is that what you expect with the external
>> surface rendering logic you explained?
>>
>> What is not clear is even if there are 2 surfaces, shouldnt I be seeing a
>> blend of blue and green?
>> And shouldnt it be same whether I see from top or flipped?
>>
>>
> That is what I was trying to figure out. I suspect you see only blue
> because those are the first polygons rendered in the object. Correctly
> rendering translucent geometry is order dependent and VTK doesn't do depth
> sorting automatically (since it takes time). Try enabling depth peeling. If
> your graphics card doesn't support depth peeling use vtkDepthSortPolyData.
> You should then see a blueish green object and that should be bluer or
> greener depending on what is nearer. However you still won't see anything
> on the inside.
>
> Bhanu
>>
>>
>>
>> On Wed, Jan 25, 2012 at 4:26 PM, David E DeMarle <
>> dave.demarle at kitware.com> wrote:
>>
>>> When you flip the object around, do you see only green?
>>>
>>> In any case, the typical mapper people use for surface rendering,
>>> vtkDataSetMapper, extracts the external surfaces. With that there is no
>>> possibility to see the inner cells even with opacity.
>>>
>>> You could instead send the data through something like the shrink
>>> filter,  to  break up the object so that all cells are unconnected and thus
>>> external. Surface rendering with opacity then might to what you want.
>>>
>>> However, it is much better to use volume rendering. That will be much
>>> faster and consume less memory.
>>>
>>> David E DeMarle
>>> Kitware, Inc.
>>> R&D Engineer
>>> 21 Corporate Drive
>>> Clifton Park, NY 12065-8662
>>> Phone: 518-881-4909
>>>
>>>
>>>
>>> On Wed, Jan 25, 2012 at 4:58 PM, bhanu <bhanu at petrotel.com> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am using VtkUnstructuredGrid to render a simple volume wherein each
>>>> grid
>>>> cell in the 3dvolume has 8 world coordinates. Each grid cell has a color
>>>> associated with it and I am using a vtkLookUpTable for this. When I use
>>>> SetOpacity(1) and see the top view, I expect to see the top layer alone
>>>> since I have set an opacity of 1.0. And that works fine.
>>>> Now When the opacity is changed to anything less than 1 (even 0.99), it
>>>> seems the top layer vanishes and all I see from the top is the bottom
>>>> most
>>>> layer.
>>>> For example, if top most layer is green and the bottom most layer is
>>>> blue
>>>> (with inbetween layers shades of lighter green), with opacity less than
>>>> 1, I
>>>> see all blue from the top. I was expecting mixed colors( green and
>>>> blue).
>>>> What am I missing.
>>>>
>>>> How do you see a transparent grid using VtkUnstructuredGrid and Opacity
>>>> property. Should I not be using Scalar Opacity for such a problem. Is
>>>> this
>>>> where one uses Gradient Opacity.
>>>> Can anyone please paste some code to direct me here.
>>>>
>>>> Thanks,
>>>> Bhanu
>>>>
>>>> --
>>>> View this message in context:
>>>> http://vtk.1045678.n5.nabble.com/VtkUnstructuredGrid-SetOpacity-tp5431453p5431453.html
>>>> Sent from the VTK - Users mailing list archive at Nabble.com.
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>>
>
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