**comp.graphics.algorithms**

## Subject: **field of view math**

Hello All,

I'm using a 3d renderer that does not allow for motion bluring FOV

changes (prman). I'd like to simulate this with a 2D filter, I think it

should be possible.

Right now I'm trying to construct a vector image where each pixel

describes a dir and mag of where that point will move to in screen

space.. then use this vector image with a vector blur operation in a

compositing package to smear my final image.

I've got a hack going right now where I view a grid in front of my

camera and project screen space coods on each point.. I do that for

currrent frame and next frame.. then generate a vector for each grid

point between the 2 frame samples. This gives me a normalized 2d

vector which I then multiply by the x & y size of the camera res. I

think this will give me a vector at each grid point that tells me how

many pixels and in what direction a screen space point will travel over

1 frame. I render this grid as a floating point image and smear my

beauty render based on this vector field.

First off, does anyone see any flaw with this? Right now I'm getting a

radial blur as I would expect, the blur lengths aren't quite right yet

but my image looks almost right.. tyring to debug if my vectors are bad

or if it a prob with the way I'm bluring. Anyway, I think I can get

this working with a bit more debuging

All this to say, I'm guessing there is an easier way to construct this

vector image without going though the renderer. A fov blur should just

be a 2d screen space problem.. should always come out to a radial

vector field where the center of frame is 0 length. So given a camera

with all the usual variables available to me.. is there a simple

formula that will tell me the screen space offset given an fov change

over time?

Thanks for any help!

daniel

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