[vtkusers] Rendering multiple actors with opacity (alpha)

[Eugene Kim]

Nevermind, what I did completely ruins things.  The order in which things 
get rendered is completely confused when using both schemes.

Eugene

On Tue, 15 Aug 2006, Eugene Kim wrote:

> Hey Michael and vtkusers,
>
> 	That definetely affects the opacity of the objects in my scene. I'm 
> rather adverse to modifying the source code, so my simple hack was to change 
> the Opacity on a given actor to .99.  Since i'm using a lookuptable anyway, 
> this has no noticeable effect on the objects, (except an occasional greying 
> due to the switching b/t color modes).  Thanks a lot, and I hope you submit 
> that change.
>
> Eugene
>
> On Mon, 14 Aug 2006, Michael Rice wrote:
>
>> Oops, there was a typo in my post. The check is if opacity != 1.0 (not 0 as 
>> in my original message).
>> 
>> On Aug 14, 2006, at 9:08 PM, Michael Rice wrote:
>> 
>>> This sounds like a problem we had. If you look in the 
>>> vtkOpenGLActor::Render() method, you see that the glDepthMask is set to 
>>> false if the opacity != 0 and the renderer is not picking. Our simple hack 
>>> was to comment out the if/else check that disables the depth check. It 
>>> doesn't produce the exact transparency we want, but it is very close.
>>> 
>>> As an experiment, you may want to try and modify vtkOpenGLActor.cxx and 
>>> see if that gets you closer to what you want.
>>> 
>>> When I have some spare time, I'd like to craft a "real" solution and 
>>> submit it to Kitware for consideration.
>>> 
>>> HTH.
>>> Michael
>>> 
>>> On Aug 14, 2006, at 7:05 PM, Eugene Kim wrote:
>>> 
>>>> Hi everyone,
>>>> 
>>>> 	I've had an annoying little problem which should have an easy 
>>>> solution.  For any given actor that I add to an assembly, modifying it's 
>>>> alpha values in a lookup table makes its opaque to itself, but only 
>>>> somewhat so to other objects.  Depending on the order in which objects 
>>>> are added to the scene (via assembly), the first object will be opaque to 
>>>> itself but no other object, the second to only itself and the first, the 
>>>> 3rd to itself the second and the first, and so on.  It's very peculiar. 
>>>> Anyone know how to get this properly working?
>>>> 
>>>> Thanks,
>>>> Eugene
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>> 
>> 
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