UDK iOS Fog Issues

stupidness19

I'm having trouble getting fog to work properly in the mobile previewer.

The look I'm going for is quite simple. Imagine a city on top of a tall hill, the hill pokes through a dense fog, so you can't see the bottom of the hill. I want the impression that it's a hill top poking through a cloud, allowing the city to receive direct sunlight.

I'm using UDK Feb 2013 beta. First I tried using Height fog and Fog Volume in separate occasions. Both were unhidden and the densities jacked way up to test fog visibility. Neither would work in the mobile preview.

I read that if you go to VIEW > World Properites > Mobile you can enable mobile fog. I could finally see fog in my Mobile Preview. However, this does NOT activate the HeightFog or FogVolume properties. It simply adds a generic fog with minimal controls, which won't allow me to get the desired effect I want.

Has anyone out there done much with mobile fog in UDK, that might know how to get this effect i'm looking for? I've been working on this for weeks!!! Any help would be most appreciated!

radiancef0rge

I think Im not positive but anything but regular fog is not available on mobile?

Hourences

Only standard distance fog is supported, no height or fog volumes.

If I understand it right you got a city on a mountain surrounded by clouds in the valleys surrounding it? I would do this by using a heavily subdivided plane that makes up the top of this layer of clouds. I would then add a tiling slightly translucent cloud texture on this plane, and I'd then vertex paint the edges away so you'd get soft edges around the mountain tops. Possibly repeat 2 or 3 times more so it gets more depth + maybe some particle planes moving through as well.

As far mobile goes that is the best I can come up.

stupidness19

@Hourences
Great idea! I'll definitely give it a try. Has this been done in any game that you can think of? I'd love to see an example if possible. I'll be sure to play around with it. Thanks for the feedback!

Hourences

I can't immediately think of any game that did that. I assume theres quite a few games from the 2000-2004 era or such that did this, but can't think of any.

I did this myself recently in our Unreal iOS game Unmechanical, with our water surfaces. It is something I also intend to cover in an iOS Unreal dev video I hope to do later this month/in may.

In general you want to use vertex colors where possible due to the bad texture compression on mobile, so alpha maps are worse than vertex colors.

stupidness19

I'm worried that 3 high tessellated planes will be hard for mobile to handle and slow it down. What do you think? Will this be an issue?

Hourences

Id start with one, might look good enough. One should not be a problem. If it is below iPad2 then 3 may cause a slow down yes. If it is iPad2 or above it probably works out.

The polycount also doesn't has to be that high. If you model it to fit the mountain, and not just go for a grid like subdivision, you can probably keep it down to just 1000 or 2000 triangles. Even if it were 10k, the polycount is not your biggest problem. Translucency overdraw is.

stupidness19

Thanks for the advice.
Have you done much with the exporting to iOS process? I've got the UDK iOS dev book. It runs through how to do it, but it looks like you have to pay 100 dollars for a developers license in itunes. I'd like to avoid paying that for now. Can I just load it straight to my iPad2 without the license?

Hourences

afaik no you cannot. That is not an Unreal limitation but an Apple thing. Unless your iPad is jailbroken...

stupidness19

ok... so i've been playing around with vertex painting. Finally got it to work between two textures, but how do I vertex paint with translucency? Is it a special node or a material property?

Hourences

What may work, and I never tried, is to blend between two textures with texture B being a tiny textures with black alpha, so entirely see through. And then set the entire material to Translucent render state.

Otherwise I tend to use Additive render state and paint black vertex color. That works well usually but if you will have several layers of clouds it may just white-out since additive adds up to white.

Note that the preview is not really accurate when you begin doing advanced materials like this. I never use the previewer.

stupidness19

So I got some see through clouds to work on a plane in UDK. I plugged a texture node into the diffuse input and a duplicate texture node into the opacity input. Boom, works like a charm. However it won't show in mobile previewer. You are saying it might actually work in real game even though the mobile previewer won't pick it up?

Hourences

Yes the previewer can't handle various advanced setups well but you should probably get at least part of it working, or at the very least you should see SOMETHING happening, even if it not entirely correct.

However when you say you "plugged it into diffuse input" it makes me think you are using the expression/shader network (drawing wires) and mobile does not use that whatsoever. It only uses the mobile section at the bottom of the material, and you will have to make do with just those properties there. Are you doing that?

stupidness19

I'm a little confused because aren't I suppose to use the material shader/wire network to vertex paint the translucency like we were talking about before?

Hourences

No the entire shader network is PC only, mobile has nothing to do with that.

You can use the shader network to see it on PC, but it will not help for the previewer or mobile.

Mobile uses a section at the bottom of the material panel, in the main material properties.