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ray tracing - motion blur

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I have not thought this question through yet but... Since I have successfully implemented the majority of ray tracing basics, I thought I would start on my “wish list”. My wish list has only one item – motion blur. So what, how, etc do I need to do to implement motion blur in a ray tracer??? Would this effect my scene definition file? For example, if I wanted to motion blur a sphere, in my input file, would specify a starting position and an ending position? What about timings? Hmmm...

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Since you've got a fully featured raytracer, I assume you're familiar with distributed rays. To implement motion blur, simply jitter your rays not by position, but through time. Give your sphere a velocity, and offset its position by that velocity vector times the time parameter. For example, you might distribute 50 rays such that their t value is anywhere between 0 and -1. Objects with no velocity are solid (no motion blur, since the t parameter would have no part in the equation). Objects with a high velocity will have a varying backwards positional offset. Then, average the results of those rays just like any other distributed method.

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Quote:

Objects with no velocity are solid (no motion blur, since the t parameter would have no part in the equation)

That does not mean that you can skip not moving object: at least you must check if the camera doesn't move.

A interesting way to implement motion blur is by vector buffering: you create a buffer where, for each pixel, you store the velocity of the corresponding object as a vector. In a postprocessing step, you blur the image using these vectors to module the blurring filter. I cannot point you to some resources, but I once saw an image produced by this effect and it was very good (Lightwave site, perhaps).

Could be an alternative for fast motion blur.

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I didn't really mean you could skip it; obviously if the camera is moving, the ray source is distributed over time as well.

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