Alpha channel problem, not showing transparency

Tom Ellis

Hey there all, having a problem with creating an alpha map correctly.

Apologies in advance if this is a no-brain problem, I've only used alpha maps a couple times before and getting them right is still new to me.

I'm working on an air con unit for a scene I'm doing, it's only a small asset but I wanted to get it looking pretty decent, but I'm utilizing an alpha map for the fan grille since it's not worth making the grille from geometry.

What I'm trying to achieve is to use a plane as the grille, which sits in front of the hole and fan, which ideally will have the grille texture in the diffuse and the alpha will 'cut out' the spaces between the grille bars.

I've illustrated the prop and the alpha I'm using below.

When I apply the alpha though, using both Xoliuls shader as well as the Max DirectX shader, with 'use alpha channel' checked, it just greys out the alpha section and doesn't show any transparency.

I'm guessing it's something to do with the plane itself since other parts of the mesh behave as expected if I put the alpha texture on a different part to test.

Any pointers on where I'm going wrong would be much appreciated! Many thanks.

Tom Ellis

Ok update,

I've tried it in Marmoset using the same Diffuse w/ Alpha and it works fine.

So it's not working in Max with either shader, however other props I've made that use an alpha still load in Max fine so it can't be a global Max setting either.

Still, got me stumped.

EDIT: Update 2,

Works fine in UDK also, as well as using a standard Max (non DirectX) shader with the alpha piped into the opacity map.

Mark Dygert

Did you check the viewport transparency settings, you might need to adjust it to best.

2010 click on the last category in the viewport label (Smooth+Highlights) and you'll see transparency. In 2009 and lower you right click that label and its right there (I hate they separated it all in 2010).

Max has never really been all that great at using the alpha channel for transparencies it likes separate maps.

I think you did this already but if you're using the alpha channel make sure to go into that maps "bitmap parameters" rollout and under mono channel output set it to alpha. sometimes you need to toggle the viewport visibility of that particular map to get it to show up.

Tom Ellis

Thanks for the reply Vig.

Yep all is present and correct as far as your suggestions go.

It's just not showing when using either Xoliuls shader or the default Max DX shader.

When using a standard Max shader, it works fine, and when looking at it in UDK / Marmoset it works fine.

The strange thing is that if I load another mesh in that uses an alpha channel, the DX shaders show it fine so it can't be a global DX setting.

Eric Chadwick

Detach the grill plane from the rest of the mesh, then re-attach it. This should set those vertices to draw last. You might have to do the opposite, detach everything from the plane and reattach. If neihter of those work, you could always simple try making the plane a separate object, then disable transparency for the shader on the main object.

Tom Ellis

Many thanks Eric, that sorted it. Just detaching the plane and reattaching it was sufficient.

What is it that causes this? Just curious so I know for next time.

Thanks again.

Eric Chadwick

There's an explanation here. Kind of in-progress though, from another recent thread.
http://wiki.polycount.net/Opacity_Map#head-2c368d1ceee6dacd2a6b5789571c136da06d9413