HI Émeric, If you want to just change the display of a small number of selected triangles then I'd suggest using a separate osg::Geometry that contains the triangles that you want to effect. This osg::Geometry would be dynamically updated as you select different triangles.
The way to get this custom osg::Geometry triangles to display in place of the original osg::Geometry is use the depth buffer to prevent both sets of triangles overwriting each other. If the case of opaque triangle it'd be easy, you could simply use osg::PolygonOffset to push the selected osg::Geometry in front of the original, or set the draw order to pre-draw the selected osg::Geometry and set the depth test to only accept LESS (see osg::Depth/glDepth), or render the selected osg::Geometry second and set the depth test to accept LEQUAL (less than or equal). You control the draw order using osg::StateSet::setRenderBindDetails(binNum, "name")); If you want to render the selected triangles transparent then you'll need to prevent the original triangle from drawing by rendering the selected osg::Geometry first with depth write turn on, but color mask set to off (false,false,false,false see osg::ColorMask) and with depth test set to LESS (for the main scene included the original osg::Geometry), and then a second pass would have the selected osg::Geometry rendered in the transparent bin, with depth test set to LEQUAL, and color mask back on. Robert. On 27 January 2014 09:29, Émeric MASCHINO <[email protected]> wrote: > Hi Nick, > > Thanks for the pointers. > > > although they are right in the book about colors being vertex attributes > I > > think You can achieve the effect You are after by using osg::Material and > > adjusting the alpha and then use a proper Blending Function. Have a look > at > > osghud example it has blended quad on top of the screen. > > If I'm not mistaken, osg::Material is part of a node's StateSet, > that's only available starting at the Geode or Geometry level. > So, altering the blending function there will impact all the triangle > faces of my model, not only the selected one. > > > If You want to show/hide then probably the best is to use setNodeMask on > > Your osg::Geode containing the osg::Geometry > > Here again, since setNodeMask is only available starting at the Geode > level, this would require that I put all the individual triangle faces > of the model in separate Geodes in order to individually show/hide > them. > Indeed, I don't know beforehand which triangle face will be selected > by the end-user. > > Émeric > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >
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