trouble creating an invisibility cloak effect in cycles


Blender user of nearly a decade here. I’m not pro but I’m not a beginner either. That being said, I seem to be having trouble getting a rather simple masking effect to occur in cycles. I’ve tried virtually every bit of advice I could find through google to no avail.

I have two planes set up that are basically line drawings with alpha channels. One is slightly hovering over the other with an object (extruded plane) sitting between the two. This plane has a shape key which I use to animate it’s movement in relation to the foreground plane w/image sequence and alpha channel (not sure that even matters for the purpose of my question). Anyway, when I was working with this scene in blender render, it was rather easy to get the masking plane to be invisible while still masking the rear plane and nothing else. Now that I am using cycles, the workflow has changed and I cannot get the plane mask to be both invisible and masking the rear plane.

I have a feeling that I should be using render layers but none of the tuts I’ve seen really address my situation nor seem to work as directed.

Any and all help would be greatly appreciated and if need be, I can post a few screenshots.

Yes, please. Screenshots.

The eyeball is a single image png with alpha loaded in through add images as planes. It is animated with keyframes Loc to move left and right. The surrounding but is another plane loaded in with same but a sequence of png with alpha, instead. The highlighted plane is just a plane extruded and animated to match the sequence plane’s eyelid blink.

My problem is that no matter which tuts or forum entries I try, none seem to work (anymore?). This includes adding a pass index, render layers, etc. Nearly all of the info I’ve found is from 2 years ago or older and I suspect the workflow has changed since. All I’m trying to do is use the extruded plane as a mask so that the outer edges of the eyeball iris donot render past the eyelids on the other plane while the mask remains transparent upon render. Heh, it wouldn’t be nearly half as difficult if I didn’t have to use this logo with alpha and I’d rather not go all the way back and do it all in the image sequence layers.

Well, I’m not sure whats happening as far as my last posts but they don’t seem to be appearing. Fist post had a link to a screenshot w/explanation and the second post had a link to another thread (unanswered from months ago) here on this forum. Maybe I’m restricted from doing either at this point because I’m new here… I don’t know. Upon checking the rest of the forum, maybe I should have this query in materials instead. I only posted in compositing because clues were leading me to believe that I might have to work with render layers.

Any guidance would be appreciated.

I’m pretty bad with compositing, here’s my shot at it. There are 4 render layers:

  1. The larger logo with alpha
  2. The eyeball with alpha
  3. An eye shaped mask
  4. The background image of ocean.

All the materials are emission, so you only need a sample or two and renders are very fast. It looks like this, have a look if you like:

Blend on dropbox

Thank you for the go at it but the eye mask needs to be invisible upon render while still masking the edges of the eyeball. I can make this work in Blender render but not in cycles.

In BI, it was rather simple to just go to material and check transparency, mask and slide the alpha down to zero. However, I have an entire animation with a model on another layer that need to be part of the same render as I will be working on making light coming through the alpha of the eyeball and top layer to cast a shadow down onto the model. I already have a test run to make the shadows cast through the alpha channels, I just need to make the eyemask transparent while still masking the eye.

here’s the blend file w/BI render:

Thanks again for the input.

Have you tried using the Holdout shader in your cycles material nodes setup? A Holdout always appears as transparent. This is different from the Transparent shader, which will show whatever is BEHIND it. A Holdout shader will always be transparent, regardless of what is behind it. Useful for compositing tricky down the road.

Thanks for the reply. I actually tried the holdout shader many times but for some reason, I couldn’t get it to work. However, After going back through for the umpteenth time and retrying stuff, I figured it out.

I made the world background transparent (the step I was missing) and then tried adding a HoldOut Shader to the mask plane. Then I ran all 3 planes on one render layer and a 2nd render layer with only a large sphere with color for background through a ZCombine. In the image I’m posting, you’ll see I actually have 2 render layers running through a ZCombine and the output from that running into another ZCombine along with a third render layer which is the background sphere.

I wonder if there is a way to bypass using the world sphere. Like making the object layer with the mask and planes have a transparent world and another object layer actually have color.

Heh… It really was grueling going through this while learning cycles. As I said, I’ve been messing around with Blender for years but never had the computing capability to really do much with cycles until recently so I was struggling with it’s properties panels, nodes and workflow. I must say, it really is worth it.

Thanks you both for the help. Photox, your Captain and Neanderthal creations are astounding! And Benu, I’ll be trying out your analglyph tuts very soon after I tidy up this project. Heh, I might even try to incorporate it into this project.

Thanks again!