Maya 4.0, Problems with Alphas in the Viewport

[jasonf]

Hello. I'm just wondering if there's a solution to Maya 4's problem displaying alpha transparency maps in the Viewport? I can render fine with a seperate (inversed)alpha file mapped to the transparency node, but in my viewport the alpha mapped to the color node makes my objects look like they have back-face culling or some sort of translucency.

It makes having an alpha channel on my color texture file seem somewhat pointless in the viewport because on a character, for example, any faces facing the camera disappear entirely when there are faces directly behind. (ie. the back of the head shows through the front of the head and vicaversa when the camera rotates around).

Anyway, if anyone knows what I'm talking about and has a fix, please let me know!!!

[raiden]

What I've found is that alpha channels on simple objects, such as primitives, will show the alpha properly in the viewport/render. But on something like a character, made up of several primitives that have been stitched together, there does appear to be some translucency issues...

I don't have a fix for you but it appears to have something to do with several stitched shapes? If someone knows a fix, I have a feeling it would make alot of people happy...!

-Raiden

[kiwi]

In reply to:
What I've found is that alpha channels on simple objects, such as primitives, will show the alpha properly in the viewport/render. But on something like a character, made up of several primitives that have been stitched together, there does appear to be some translucency issues...

I don't have a fix for you but it appears to have something to do with several stitched shapes? If someone knows a fix, I have a feeling it would make alot of people happy...!

-Raiden

I remeber seeing aplha channel display issues in the hardware qual. charts on the A|W site. -seems there are some limitations with some 3d cards not displaying alpha channels correctly.

kiwi

[warpcat]

Undocumented "feature" or bug, you make the call. Basically, if you have an image mapped into the alpha channel of a .tga (other formats too?), Maya (Open GL perhaps?) will source that channel as "opacity". This is a different term than Maya's shader "transparency", they are two different things. The problem is (this is a big issue with game engines too) Maya dosen't know how to sort the pixels that have opacity associated with them. If your image has alpha, whether or not those pixels actually define a opaque or transparent region makes no difference, they do define the STATE of opacity, meaning every pixel in the map has some kind of opacity. So what you end up with is a surface that can't decide how to sort it's pixels in OpenGL. The workaround... well, remove the alpha... If your surface never curves behind itself, you won't notice the issue, but when you have multiple surfaces with opacity intersecting, the z-sorting becomes apperant...

[jeffd]

So here is the workaround that was alluded to in an earlier post. Go into your material and rollout the hardware texturing frame. Change the Texture Quality from Default to one of the other settings. This should make you opaque again and z-sort properly. Granted, no more alpha in the viewport, but at least you don't have to maintain two versions of your texture. Other downsides to this is that you lose resolution most of the time and loading the file will take longer as Maya creates BOT files internally for that texture. Not bad if you only have one, but bad if you has a dozen or so.

--JeffD

[warpcat]

Right on! I love these forums. Knowledge exchange GOOD.
Guess I learned my one new thing for the day
-Eric

[jasonf]

I appreciate all the advice and quick responses! Thank you!

Well, seems like we'll all hafta wait until version 5 for a true fix... somewhat disappointing, but I guess alphas in the viewport are a bonus anyway.

If anyone can come up with any sort of fix in the meantime, let us all know!

~JasonF

[firas-ershead]

its not a bug

just expand the faces into objects and gorup these faces ..

i wish i have time to explain it .. maybe onther time

firas

[jeffd]

I think I have an idea of what you are getting at...

Are you saying to break the model into a separate object for each face, then group all those faces. I would think that might work, but at the expense of ease of being able to continue working on the model as well as destroying any edge smoothing that might have been setup. I don't think that is a good trade for me.

But maybe I misunderstand your approach.

--JeffD