Making a sprite emitter or hair emitter disappear

[Eric2575]

I've read several post in which people were noticing that the emitters were not totally transparent when a scene was rendered. Well Nancy shared a little trick with me in one of my posts that I thought was good enough to share with everyone. Many of you may know this already, but some may not. If you want to make an emitter disappear, here's the trick: Make a small TGA image with a transparent background and an alpha channel for the whole image. When rendered in AM you should see nothing. Now take that TGA and apply it as an image to the emitter mesh you want to hide. Here is the kicker: in the image properties under the mesh shortcut, change the property from color to cookie cut. That's it. Now when you render the mesh, it will be completely invisible. Please note that I've only tried this with hair meshes, but I believe it should work on sprite emitters too.

 

Koodos go out to Nancy for this neat little trick.

 

Eric

[robcat2075]

fabulous info.

 

Thanks, both of you!

[Paul Forwood]

Good trick. I have experienced emitters that wouldn't respect their own surface properties' transparency settings in the past but they do seem to be working alright at the moment.

[mtpeak2]

You should be able to set the group transparency to 100% to make it invisible, but you also need to set the transparency to 0% in the hair emitter to keep it visible.

[Darkwing]

setting an object to 100% transparent is actually the problem I believe Eric has fixed here. When you set an object to 100%transparent, the particles cause peculiar rendering artifacts, usually black lines that resemble the wireframe (this is in final mode and is a problem with apparently all versions of AM) I will have to try this trick as I've been looking for a fix to this for years

[mtpeak2]

I don't see the issue you are referring to.

[Darkwing]

it occurs with particles only to my knowledge, hair, streaks, fluid and blobbies to my knowledge all work fine

[mtpeak2]

Still no issue with sprites.

[Darkwing]

this is what I get when I do particles and apparently many others do to as I've brought it up before a while ago. It's at the bottom of Earth. The first pic was without multi-pass, the second with I do believe. I remember this because I believe it got worse with multi-pass

 

 

[Darkwing]

as the earth pic was from v13, here's what V15's version of the particle issue looks like:

 

[Darkwing]

And using the cookiecut method Eric described:

 

 

due note that the transparency issue is fixed when rendered in shaded mode as opposed to final. That unfortunately has some of it's own issues, one being the fact the coordinate thing (forgot its name) shows up in the bottom left.

 

EDIT: One more quick thing to note that I just tried, this only happens to the emitter. I threw in another transparent sphere (not using cookie cut method) and the particles did not effect the sphere. The sphere was completely transparent, the emitter retains that unusual blemish

[mtpeak2]

Do you have a project you can post?

[Eric2575]

So the issue is still not resolved even with the cookie cut method. Darn.

[johnl3d]

I tried it

 

sparks.mov

 

 

watch the color change especially when there is nothing behind the emitter you can see the curve

 

 

so the problem is still there

[Paul Forwood]

Hmmm. Could this be something to do with the alpha channel? It reminds me of a problem that I was experiencing some time ago when rendering cookie cut imagery against an empty background.

What do you get if you render inside a skydome?

[Darkwing]

one of the things I found in my travels with regards to the particle rendering problem is that it has been there since some of the oldest versions of AM. Funny thing is that each time a new version is released, the issue changes and renders differently. And to test the alpha channel thing, I'll make a solid square particle and see if it renders the same

[mtpeak2]

I guess noone has a test project? I still don't have an issue.

[NancyGormezano]

I don't have a project - but if I look at John's example movie here - I see that when the transparent emitter and a sprite image with an alpha channel occlude - there are artifacts. Not sure if the sprite is in front of emitter or vice versa in his example. It does not seem to matter if the sky or ground is the background.

 

I'm guessing that John was using a sprite image that had an alpha channel, as well as that the emitter surface patches were made 100% transparent (not sure if he did it with setting surface property or with a cookie cut patch image)

 

EDIT: - maybe it's also related to having additive color =ON as well?

[mtpeak2]

I understand that Nancy, but I don't get these artifacts. That's why I asked for a project (and image used) to see if I get them and to see if I can track down the problem.

[Darkwing]

yeah, i'm packaging my project up right now

[Darkwing]

here we go

 

Particle.zip

[mtpeak2]

Very strange, never seen this before. Yes, I'm getting the artifact and can reproduce it. It's very odd, I'm getting it using a flat plan as well. It looks as if, whether the sprite is in contact or in back of the transparency, it is being shifted on the final pass (non multipass and multipass), like it has an IOR set or something.

[Darkwing]

yeah, now humour me and render it in shaded mode as opposed to final

[mtpeak2]

Shaded render is fine.

[Darkwing]

yes, that was the same result with me. Unfortunately using shaded render isn't exactly a good option when making scene with other elements in it. I wonder what's different about the shaded render vs the final render engine for particles? Perhaps it can be adapted into the final renderer? I posted this a while ago on Am Reports, but never got a response

[Eric2575]

Well, at least we are all on the same page now

[robcat2075]

As i see it, the artifact is at the intersection of the sprite with the emitter. Only the portion of the sprite that is on the viewer's side of the emitter surface is visible. This is apparent by spinning around the model when a particle has a portion on both sides ( I deleted the back half of the sphere so i could see inside)

 

We should be able to see the whole particle thru a 100% transparent surface, but we don't. It's getting clipped.

 

 

Possible work around... make your sprites 100% transparent at the beginning of their life and fade them to 0% transparent after some point when they would have cleared the surface of the the emitter. Haven't tried this.