As far as I’m aware, it doesn’t (by default, at any rate). The micropolygons are shaded at one specific moment of time, with everything assumed static, and are then blurred across the image.
In other words the shading is spatially inaccurate for something like a fast moving object going through a tunnel with overhead strip lighting?It is inaccurate, yes (again, by default; there may be a way to get the correct thing).
An easy test for this is to get e.g. a rotating propeller viewed and illuminated from the front, so that the propeller blocks its own shadow. If shading is correctly motion blurred, you will never get to see the shadow itself, since it is at any one moment blocked by the propeller. However, PRMan normally computes the shading and motion blur separately, leading to an incorrect result.
Here are some tests done with 3Delight as an example where I’ve made a rotating red box with a spot light that casts blue shadows. The correct result as rendered with V-Ray is to see just the red box (since it almost completely occludes its own shadow). But 3delight calculates shading first, and then does the motion blur so you can incorrectly see the blue shadow behind the box. (It may be perfectly possible to get 3delight to render the correct image, but I don’t know it well enough to do that.)
Of course, this may or may not be an important difference (in many cases it isn’t).
Best regards,
Vlado
