| Re: overlay a 3D polygon on a 2D grayscale image? [message #31938 is a reply to message #31871] |
Thu, 29 August 2002 16:53   |
Chunlei Liu
Messages: 4
Registered: August 2002
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Junior Member |
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Thanks for the tip... I could see both of them now. But I don't know how
to make the polygon semi transparent. Right now it's not a problem for me,
since the polygon is small...
Chunlei
On Tue, 27 Aug 2002, Rick Towler wrote:
>
> "Chunlei Liu" <chunlei@stanford.edu> wrote
>>
>> I have a 3D polygon and a 2D grayscale image. I am trying to overlay the
>> polygon on the 2D image, so I can see the image through the
>> semi-transparent polygon. Also, I am NOT intending to use the 2D image as
>> a texture map.
>> I know David Fanning's website has an example of blending two 2D image
>> together using alpha channel. I tryied to make the 2D image transparent (
>> which is not what exactly I want), so I can see the polygon, but seems
>> like it won't work that way.
>> Appreciate any help....
>
> This could be a number of things.
>
> First, make your polygon a wireframe.
>
> How have you ordered your objects in Z and how are they ordered in your
> model? I would assume that you have the correct Z data coordinates placing
> your image behind your polygon... Objects are drawn according to their
> order in which they are added to the OG hierarchy. This means you need to
> add atoms from back to front in your scene. If you have only a single model
> make sure that you add the image first, then the polygon.
>
> Do you see it now? If so, change your polygon to a solid and test your
> alpha blending. Can you still see it? If not, google this group for
> "Pimento Problem" to find an detailed explanation of how IDL renders
> individual atoms and its importance when texturing with an alpha channel.
>
> If you still don't see it make sure your view is set up correctly (maybe the
> polygon is behind you?). In fact, try using xobjview to view your model.
> It scales the view automagically.
>
> -Rick
>
>
>
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