Preparing Scene Data

I’ve never had this before, but when I render a scene with large amounts of hair particals, whether they are in the render or off screen, i get a black screen at the beginning of the render saying “preparing scene data” for several long seconds. When the image finally begins to draw it renders very quickly, it just takes blender several seconds to start rendering. But this only happens when I have lots of particals, and it doesn’t matter if the particals are in camera view, or not.

Is this normal? If so, how can I speed up partical rendering time, or this preparing scene data phase of the rendering process?

This usually has to do with ray tracing and shadow buffer calculations which happen in a pre-process, i.e. before the actual render. Properly setting up your octree can minimize calculation times.

This could also be Blender converting your vertex points into strands or splines with their associated curvatures (actual geometry) before computing a depth buffer for them.

Indeed, that’s Blender figuring out what to do with your strands. Not much you can do to optimize it other than to strictly control your strand-emitting objects in the Scene. In other words, if they don’t appear on camera, you can eliminate the “problem” by disabling the Render button on that particle system – either in the particles panel or the modifiers panel. It’s little more work, but if you’re rendering an animation it will save you a bunch of time.

Thanks for the replys. So its possible, like for an animation, to have the camera say, viewing grass, then maybe move out, maybe to the sky or something, and disable the particals on the ground? I guess I would need a script or some kind of timer?

And thanks for the link about the octree. I’ve heard about it, but never looked into it, so now i’ll read up on that!