Rendered boolean mask

[Matthew Murrian]

Hi,

I have the need to render a boolean mask of a scene; an image with 0s for background/transparent pixels and 1s for "foreground pixels" (and no anti-aliasing, 1s or 0s). Of course, I could create a boolean mask myself from a normally-rendered scene... set the background color to black and replace rendered non-black pixels w/ 1s. However, it seems to me that the entire cull/render operation could be streamlined quite a bit with the end goal taken into account.

Can anyone recommend an efficient way to render a "boolean mask" directly? Forgive me if this is a common feature and I just don't know the lingo to find it.

Thanks,
Matthew

[Matthew Murrian]

Update: I've found the Stencil functionality and have determined how to use it to generate the boolean mask I require (and then copy it into my own buffer through glReadPixels). That resolves half of my question.

The other half is to whether there is a more efficient way to use OSG/OpenGL when I only need to render into the stencil buffer (i.e., I don't need the color or depth buffers). As it is, I am rendering into the color buffer but ignore the results. It would be great to reduce computational effort to the minimum required to populate the stencil buffer alone.

Thanks again,
Matthew

[werner.m...@modenbach-ac.de]

Hi Mathew,

what about creating a texture with black for false white for true. Map this texture to a quad and set it to "nearest" mode.

Werner