Now that we have an Ambient Occlusion node it's possible to create shaders that automatically fill nooks and crannies with dirt. The image above shows four basic AO based dirt shaders. I've rendered without shadows so you can see exactly what the shaders look like without any lighting effects. In the next few posts, I'll show you how the shaders are built. Essentially, AO is used to tell the shader which bits of the model should have dirt on them.

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Here's the node layout for the first shader. This one is the floor of the first image. The shader starts with the ambient occlusion node, which we then filter through a math power function. This takes the square root of the AO output, which just softens the transition between light and dark areas of the AO node. After that, we subtract the output from 1 with another math node. This just inverts the colour, so now we have white in the places where we want dirt and black in the places where we don't. From there, we take the output to the bias parameter of a clouds node. By doing this, we tell the clouds node to make white cloudy bits where we want dirt and blackness everywhere else. Finally, we use the output of the clouds node to drive a blender, with dark green for dirt and white for clean areas.

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Here's the next one (the right hand wall this time). This one uses fractal sum instead of clouds. That's really the only difference.

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This third shader is the one used on the left hand wall. It's a little more complicated than the others. This time we use use an fBm node for the dirt noise. I've set it to use the new Improved noise type because that gives more attractive noise. However, this introduces a problem because the new noise type never gives complete blackness, even when the bias is set to zero. To compensate for that, I'm running the inverted AO output through a math step function that will tell the shader where there should be no AO shading and then multiplying that with the fBm output to make sure that no noise appears in areas that should be dirt free. Without this step, all areas would have at least a little dirt.

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Last one. This is the shader used on the ball. It's just like the previous one, only using turbulence instead of fBm.

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Very Nasty Very Bad bad BAD!! shadow. Not all corners r supposed to get AO

Here's that first render again, but with some of P6's nice new lighting options turned on (one point light with ambient occlusion lighting turned on). Remember to turn on raytracing any time you want to use ambient occlusion (whether it's for lighting or for shaders). AO won't work without raytracing.

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is there any render speed difference with any of these settings? Since they all look "good", whichever one renders the fastest might be the choice one. (not sure how much math increases renderspeed)

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nice work Ajax can you make it smaller more subtle?

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GWeb, actually if you take a look at the mathematical procedure behind AO, yes all corners are supposed to get it. That's how the AO algorithm works and it's also one of the reason AO is far from a perfect solution for true radiant lighting. Gareee, Not much difference in speed between the four shaders shown, no. It's just a matter of which noise pattern you like the best. Stonemason, Yep, you can make it smaller and more subtle. The size of the individual dirt grains is controlled with the scale parameters of whichever noise node you use. The density is controlled with the bias parameter on the same node. Controlling how far the dirt extends from the corners is a matter of filtering the AO output through some math nodes.

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Here's one more pic. This one shows how it looks when you apply these principles to more realistic shaders. The same four noise types are being used in this render, though with some parameter tweeks to make the dirt just a touch less strong.

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Attached Link: http://www-viz.tamu.edu/students/bmoyer/617/ambocc/

More info on Ambient Occlusion http://www-viz.tamu.edu/students/bmoyer/617/ambocc/

I wanted to see what those shaders looked like on a more detailed model, so here's Stonemasons Whispering Wall with the shader from the left hand wall applied to the face.

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get that bump out of the gradient slot!!..lol :) it's a nice effect with the shader,it looks a bit grainy,& obviously made up of dots..is there any way to clean that up?

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Attached Link: http://www.metafex.net/cinefex/tutorials/dn/

It's meant to be grainy and made up of dots. It pretty much matches the appearance I was trying for, rather like the grainy dirt you see in the bottom right couple of pictures on the linked page. Those were done with the old C4D DirtyNuts shader. What sort of look did you have in mind? If you've got a pic, I'll see if I can come up with something similar.

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By the title of this thread I thought I was going to have to suggest that you turn on the nudity flag. LOL

I'm not sure what I'm looking for,just less apparent dots I guess,can you control the amount of dots?..make it alot more dense but keep the opacity http://www.maxon.net/pages/products/c4d/r85/images/dirt_nodirt.jpg

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I thought he'd been running around the back yard naked again ;P

Stonemason Excellent link!! you have made my point acrossed!! Thanks!!!!!

Looks doable. Just a matter of spending lots of time tweaking I think. Let me see what I can do.

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My suggestion is to have AO shading interact with property shading for color balancing. I wish I downloaded P6 stead of Box but I want a copy of book and a pretty box hehe.

Stef, Is any of these closer to what you had in mind?

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Top right is better but not satistified. After looking at all of these. AO is not supposed to look dusty. AO is supposed to slight decrease or increase color temperature along with shading.

Can you match AO color with the sphere's color shading? I also would like you to make another sample like this but with lighter color in AO setting. GWeb

GWeb, I realise the title of this thread, containing the rather subtle words "dirt shaders", might not have given it away to you, but the whole point of what I'm doing here is to use AO as a means of filling corners with dirt. I had hoped that the very first sentence in this thread ("...it's possible to create shaders that automatically fill nooks and crannies with dirt") might have hinted that, but apparently I was being too obscure. "AO is not supposed to look dusty" Surprisingly enough, DIRT IS SUPPOSED TO LOOK DUSTY! Perhaps I'm still being too subtle, so I'll quote your own words from post 6 back at you: "Very Nasty Very Bad bad BAD!!" If you aren't interested in shaders that look dirty and/or dusty, please do us both a favour and go and find a thread that isn't about dirt shaders.

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Xena, LawnDart, I saved my dirtiest pair of balls just for you two :-)

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Hehe, now the entire of Poserdom can use the old Ambient occlusion for "dirty shaders" trick Renderman users have had for some time. Good to see we're spreading the love grin I personally like the top left, the top-right is nice for say a "tarnished" look, but the top-left really does the "dirt thing" for me,

Ajax, This is outstanding. I agree with Eternl Knight on the dirt effect preferences. I have a couple of questions:- a) Would this work for bump and displacement mapped detail? b) Although not strictly 'dirt', but coming under the heading of 'weathering' would it be possible to use the settings on the ball at top left with a rusty colour, and the settings on the ball at top right as is, at the same time, to create a rusting dirty ball? Cheers Ian

Yeah, it's something I've wanted to see in the material room for a long time :-) I like the top left too, but I think I like the bottom right just a little better. I actually only put the top right one in as a control. There's almost no dirt in it at all.

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Ian, Yep, sure will work for bump and displacement :-) Basically it drives a blender, so you just blend your dirt bump against your clean surface bump. Layering dirt AND rust will make the shader more complex with a bunch more nodes so it will be more difficult to manipulate in the material room and will render slower, but it's certainly doable. In the longer term I'd like to put together some more complex shaders like that. I'm really just playing with my new toy at the moment.

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Imagine this in bronze, with verdigris instead of dirt. Yum.

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The head looks great in pewter. Thanks for answering my questions. Can't play until my Wait-Club membership expires .... Ian

Ajax..the top 2 are spot on! Cheers Stefan

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I have visions of naked Jessis in very very dirty temples... :D

Ajax, this is outstanding! thanks for sharing!! ----- stewer! lol :P

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can you screen cap the top right settings? That looks like it would be good for victorian ship and vehicle renders. (it'd probably look nice on the martian tripod from Daz, or the Nautilus from Daz as well...)

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the top right settings are great! I agree with you Gareee and wish Ajax can share with us the setting too ;)

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Ajax - Absolutely bloody brilliant!! I love them ALL - please please please release a "Dirt Pack"!!! Wow!!

Hmm I just had a thought... if you applied negative math nodes, couldn't this be converted to some kinda of highlight lighter spots type of shader setting?

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Can this be used to make a brisk texture look dirty? (Each individual brick, as opposed to only the corners of the mesh) Also please post a screen cap of the settings you used for the balls. Excellent use of the node by the way. Creative use like this could eliminate the use of textures for much of the structures within a scene.

Something that would be really cool in poser, would be adding the ability to "bake" these on textures, and then save those textures. It's using in lightwave all the time to create actual texture maps. Since the P6 material room is really blossoming, that would be a way to "share" the new tech with the older poser version users. Not that I think it'll happen...

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Gareee, I agree fully on the Victorian vehicles, a particular interest of mine. Bring on the rivets, coach-bolts and leaf springs! Ian

Hmmm I'm also wondering, if this was included in a toon render, if it could be used to create a "stipple" drawing effect? Animated, that might be killer!

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Ajax, s always, the master of material nodes! This is a great piece of work, thanks fo rsharing! I cannot wait until I have to stop waiting }-) Shogakusha

Ah, another thought.. maybe this could be combined with the slime shader as well? I want my P6... >whine

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Garee: "Hmm I just had a thought... if you applied negative math nodes, couldn't this be converted to some kinda of highlight lighter spots type of shader setting?" Perhaps to simulate the shiny spots on larger bronze statues, where they've been rubbed by the hands of thousands of visiting tourists...?

Ajax, Yeah I wasnt interested in dirt shader. I was interested in just the AO shading that interacts the lights. Your method for dirt shader is indeed good ones. GWeb

Umm after looking at images and I reviewed AO function. The AO is supposed to be sensitive to the light that may affect the dirt shading. Just thought you might like to know.

Here's a screenshot of the settings for the top right shader, as requested. Control your dirt colour with Blender 3. Control your metal colour with Blender 4. The spread of the dirt is controlled with value 2 of Math Functions 5 (up for wider dirt, down for narrower dirt). Math Functions 3 controls the roughness of the edges of the dirt. Change both values at the same time, but keep value 1 exactly 1 higher than value 2. Notice the granite node feeding into Math Functions 4? For dirt like the top left ball in post 22, feed a turbulence node into Math Functions 4 instead (leave the granite node alone for the other things it drives). You'll need to adjust the scale settings of the turbulence node when you do that. I'll answer a few questions in a mo.

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God bless your dirty balls sir!

Can this technique be used to do things like putting shiny spots on exposed surfaces, add speckling to toon shaders, control slime locations when combined with my slime shader, etc? Yes it can. There are some drawbacks however. While the AO algorithm is as good for finding exposed surfaces as it is for finding protected surfaces, the implementation of it in Poser 6 appears to be geared toward protected surfaces. I don't think it can tell the difference between a really exposed bit, like the end of a nose and a moderately exposed bit, like the middle of a forehead. "Can this be used to make a brick texture look dirty? (Each individual brick, as opposed to only the corners of the mesh)" Not really. This approach is really for putting dirt in protected corners. If you just want dirt evenly spattered over each brick, there are ways to do it and they're probably easier than this approach. Texture baking? I wish. I don't expect it to every happen in Poser though. Still, the fact that I can make stuff like this for P6 users makes me very happy. Will there be a dirt pack? Not sure yet, but certainly I'm always storing away shaders and it's probably getting to be time I did some more shader packs. I want to take a look at some of the other new nodes first though. They quietly introduced a bunch of new rate of change variable nodes that look really interesting. I'll have to see what I can do with those. If they work how I think they do, I should be able to use them to colour sharp bits differently from blunt bits. Thanks for the interest, everybody. Enthusiastic people keep me going :-)

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Any ideas for using the new Variable nodes ?

Here's some dirty chrome :-) Gee, I really better put this down and go and do some work. "Any ideas for using the new Variable nodes?" Yeah, but only vague ideas at the moment. As I was saying, they should allow you to tell areas of rapid surface change (ie sharp bits and creases) from areas of slow surface change. They all seem to be UV map dependent, which limits things a bit. My idea is to use the U and V rates of change to get a sort of average local rate of change and then use that to drive a blender so sharp bits get one colour and blunt bits get another. Average magnitude of the two should do it.

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OOO I like that dirty chrome as well.. I think you need to make a pack of the materials you've created already.

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Ajax, your big free pack of P5 shaders really helped me solve some problems and taught me a lot. Now this article has me fired up to go make some pristine props really filthy! Many, many thanks! :D

Could you post the material seting for the dirty chrome? I LOVE that!

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Gareee, Settings for dirty chrome are above, as requested. The reflection map is one of the IBL probe images that come with P6, but pretty much any reflection map you like will do the job. The key thing going on here is that AO drives the reflection value and it's inverse drives the diffuse value, so you always have diffuse + reflection =1. madmaxh, Thanks :-) I really like to hear that people get right into those shaders and learn stuff by looking at them. That's what I really wanted that set to do - make the whole process of figuring out the material room a bit faster for people.

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I had a feeling there would be more to it then just adding reflection like P5. Thanks much for the explanation, and shot! BTw something I thought of this morning.. is there a math setting set that could be used to just remove color saturation from a material setting?

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Ajax..I tried this today & it worked quite well..how would we go about adding this setting to an already textured object? Stefan

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I'm just guessing, but maybe insert a second blender node at the begnning, and have one half of it oint to the texture, and the other half connect to the existing blender2?

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Gareee, For desaturation, just run your coloured input through a maths node and add 0 to it. That'll convert it to black and white. Stef, Just plug your texture map into input 2 of blender 2 (ie the blender that drives the diffuse colour). You can also use blenders to drive the spec, bump etc if you want. You drive the blending on them with the math functions clamp node, exactly the same way as the blender for diffuse. On each blender input 1 is dirt and input 2 is clean. The principal in the shaders I've shown here is simple when you break it down. There are three groups of nodes in the shader. One group provides colour for the clean areas, one group provides colour for the dirty areas and the final group is the AO that drives the blending between dirty and clean. If you want to add bump (for example) to the mix, it's just a matter of coming up with a group of nodes for clean bump and a group for dirty bump and then blending them with the same AO you already have, then plugging the blend into the bump channel of the root node. You can do that for as many different characteristics as you want (spec, ambience etc), just driving the blend each time with your original AO group.

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That simple, huh? Man, you need a major in math to know what's going on with the nodes.... ;)

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Scary thing is Garee, you are almost right. Writing good shaders requires a decent comprehension of mathematical principles. I have coded Renderman shaders and let me tell you - they can become really complex mathematically and code-wise. Poser (or really Firefly) gives us end-users a very good sub-set of Renderman's power with a MUCH easier interface. Trust me, Ajax's skills can come at a decent price in the graphics industry (look up "technical director" roles sometime).

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Really cool dirty shaders ! Very usefull !