The reason I'm asking is because I'm thinking of using it in a program drawing groups of 3d objects. The reason I think I need to be able to use dynamic_cast is because I want to be able to group different kinds of obejcts into the same group and access the different types of information and other stuff that is special for that type. The usuall stuff. I think I can work around it, but it would be messy.

So I would only need to use dynamic_cast when inserting the obejcts and things like that, and that does not happen much. It is the rendering that takes all the computing time and happens when the user transforms the object. I don't need any dynamic_cast in the rendering functions.

But does the use of RTTI give me time penalty when rendering the 3d images, even if I dont use any dynamic_cast in the rendering functions?

If not, then it doesn't matter much how long it takes. But if it is, then it can be trouble. Many of the images have a lot of polygons. So I need all the computing time I can get to render smoothly when spinning the object.