How Long is Too Long for Rendering?

I have about 4G of RAM on my system (please hold your laughter for the end of this post) with a fairly decent video card. Whenever I render with approximate ambient occlusion on, it takes forever to render, while it takes only a few minutes to an hour to render with ray-trace AO. By forever, I mean that I press F-12 in the afternoon, let it run overnight, wake up in the morning and eat beakfast, come back, and the render is still stuck on “AO Pre-processing” without a single pixel rendered. :eek:

The image that I typically render isn’t a scene you’d expect an expert Blender artist to render, but it does have its fair share of transparent and reflective objects. The image size ~1000 x ~1000 pixels.

Is it normal to wait that long, or am I just impatient? :mad:

Render time is based on the complexity of the scene and the materials within it. If you have a lot of transparent objects and reflective objects, the calculation of bounces and IOR increases where as it won’t with diffuse materials. Image size that you state isn’t really that big, but without the processor specs, and more importantly, the scene, it is hard to determine where the problem might be, and what the correct solution to this problem is.

why are you using approximate AO in the first place? Ray-trace is more accurate.

That also indicates some problem. I dont think preprocessing should take that much long for even fairly complex scenes.

Is it normal to wait that long, or am I just impatient?

Your question comes under the “how long is a piece of string” category. It’s impossible for anyone to answer given that no-one except you has access to your blend file so no-one except you knows how complex your scene is, so no-one except you know whether the render time is reasonable or not.

As far as I know, Blender doesn’t use the gpu to render, what is the power of your cpu?
Also, I rarely notice the difference between raytrace AO and approx AO, but that might just be me. However, I do find it strange that your approx is taking longer than your raytrace
Lastly, as marklew said, it is hard to see if its something wrong with your scene if we can’t see it ourselves.

If you have passes at more than one then the preprocessing time will skyrocket.

Frankly, the AAO was originally intended as a non-raytraced alternative to traditional AO as it would trade some accuracy for speed, you can use it for some GI bounces in 2.5, but it doesn’t do shadowing and will not show up in raytraced reflections and refractions (in part would be difficult to impossible to fix properly due to BI’s antiquated shading system).

If you just set passes to 1 and bounces to 0 or 1 you should be fine, but if you need GI then the good news is that a new GI-based, node based render engine (Cycles) is being developed as a candidate engine to replace BI entirely in the future (which has a modern, clean design for the shading and lighting code and will do away with pre-processing)