Thank you very much for such an elucidative and prompt answer!
I knew the FBO way but since this is for a cluster with not-so-recent GPUs,
that alternative is was early declined.
With this need for changing every material in the tree to support the
stencilChunk, I opted for another approach, yes a third one. :)
I sorted the viewports with the map being rendered first, into a
TextureGragForeground. Then the object in the main viewport used the texture
in its material with the proper UVs. It's working really well without
changing too many things (this is a big project on tight schedule, the KISS
approach is always welcome).
Anyway thank you very much for the answer. I may need to use this in the
future anyway!
On 9/19/07, Carsten Neumann <[EMAIL PROTECTED]> wrote:
>
> Hello José,
>
> José Pedro Dias wrote:
> > Hello to you all. I'm posting this after leading the most relevant mails
> in
> > this subject and taking a look at the examples provided in the source.
> So
> > you know :)
> >
> > I have two viewports, the second of them smaller, kind of a bird's eye
> view
> > map.
> > I already have them the way I want, except for the fact that I want the
> > smaller one to have a shape other than a rectangle (circle, in fact).
>
> using plain OpenGL you'd probably do the following:
> 1) render the circle form with the following stencil settings:
> Func: GL_NEVER
> Value: 1
> Mask: 0xFFFF
> OpFail: GL_REPLACE
> OpZFail: GL_REPLACE
> OpZPass: GL_REPLACE
>
> 2) render the scene with the following stencil settings:
> Func: GL_EQUAL
> Value: 1
> Mask: 0xFFFF
> OpFail: GL_KEEP
> OpZFail: GL_KEEP
> OpZPass: GL_KEEP
>
> For OpenSG that translates to:
> - create two stencil chunks, one for each of the above settings.
> - add the first one to the circle's material
> - set the ClearBuffer for that stencil chunk to 1, to clear the stencil
> buffer before the circle is drawn
> - set the SortKey of the circle's material to a negative value, to
> make sure it is rendered first
> - add the second stencil chunk to each material in the scene
> - render the small viewport
>
> For your large viewport you need to set the StencilFunc of the second
> chunk to GL_ALWAYS so that it does not affect that rendering. That
> however means you can not call Window::render because it will render
> both viewports in one go without giving you a chance to switch the value
> in the stencil chunk. But you can just do the calls Window::render
> issues "by hand" (it is not much) and insert the value change between
> them.
>
> The ClearBuffer field of the stencil chunk is a bit tricky as it allows
> clearing that buffer during rendering. However due to the state sorting
> OpenSG normally performs this becomes quite unpredictable. For your case
> you only need to clear the buffer once, before the circle shape is
> drawn, so the combination of a negative sortKey and setClearBuffer(1) is
> sufficient.
>
> BTW for drawing the circle shape you might want to look at the
> PolygonBackground.
>
> A different solution to your problem would be to render to "map view"
> with a FBOViewport and draw the generated texture with a
> PolygonForeground over the main view.
>
> Hope it helps,
> Carsten
>
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--
José Pedro Dias, n.48296, LEIC Tagus Park
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