View Full Version : refraction distortion pass?!

04 April 2005, 11:55 AM
I guess being related to compositing ill fire this off here.. although also being 3d related.

How does one do glass in composite layers. as ther would be no distortions from refractions. Is there a means to get a dplcament pass or similar to use in the composite behind the glass layer plate - so the image behind distorts?

04 April 2005, 03:43 PM
yep lots of ways to do this depending on how accurate you want to be. I often get good fakes by getting 3d to give me fresnel pass with different colours eg r and b used to desribe axis x and y. In this way it is kind of like a normal to camera pass but not true, this is then plugged into an iDispalce and iBlur pass which allows for induvidual displacements per axis. rememner to add some blur too ....

There are a number of ways that you could implement a true normal based solution to this but it would probably require some scripting in the old colourX and displaceX node and that means slowdown !!

Here is a simialr pipeline generated by the turtle renderer to create reflection distortion in shake

04 April 2005, 03:45 PM
ooops forgot to add the most common and easiest way which is to get the 3d renderer to do the displaced bg pass by simply feeding the bg plate into the render and turning off its primary visibility and turning on visible in refractions !

04 April 2005, 03:58 PM
lol thanks. That last seems the easiest but also the least fexible. I dont composite in shake but will see if i can make sense of it in combustion or after effects if possible. I get to theroy somewhat but as how to even being doing it - well that will eb the fun bit. Ill probably be back when the time comes to do such a task.
I was just curious as to how this could be done, as i know i have a glass shot for an animation im doing and really will need post flexiblity on this one :P


04 April 2005, 04:08 PM
I once had a tricky little requirement to show a distortion ("another world") only in an animated looking-glass which was passing over the face of the scene. (Fortunately the glass did not have to act as an actual, correct lens.)

So what I did was to do a distorted view of the entire object, and a straight view of the entire object. Inside the glass I put a circular plane. And I simply told the computer to select from the un-distorted background everywhere the pixels of that plane were not, and from the distorted layer everywhere they were.

It wasn't optically-accurate but it did allow me to achieve the effect quickly and it spared me from any re-rendering time when the path of the looking-glass across the frame needed to change, as inevitably it did.

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04 April 2005, 04:08 PM
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