Cast shadow onto a transparent rectangle geometry. Transparent shadow catcher

General TouchDesigner Discussion
1

I have set up a scene with an animated geometry with lights pointed at it. I put a rectangle below it as a surface to catch the shadows , but I want the rectangle to be transparent, and only show the shadow. I have discovered a way of doing this by using a few stages of levels and compositing to filter out the rectangle which works ok for only one surface, but wondering if there is a more straight forward solution which would be more flexible/ involve transparent geometry(s) which will reflect only the shadows cast by the light on the main geometry. Anyone know how to achieve this ? cheers!

2

I have created a file to show what I want to achieve. but “Sorry, new users can not upload attachments.” so I have uploaded it here :

https://chrispetro.net/stuff/shadow-catcher.toe

basically what I want to do is hide the rectangle but show the shadow which is cast onto it. cheers,

here is an example showing the desired result with the levels and compositing ,

https://chrispetro.net/stuff/shadow-catcher-composite.toe

but I am searching for a more robust solution if one exists

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I was just looking for this. Thank you!