Stumbling Toward 'Awesomeness'

A Technical Art Blog

Friday, January 18, 2013

Moving to ‘Physically-Based’ Shading


At the SIGGRAPH Autodesk User Group we spoke a lot about our character technology and switch to Maya. One area that we haven’t spoken so much about is next-gen updates to our shading and material pipeline, however Nicolas and I have an interview out in Making Games where we talk about that in detail publicly for the first time, so I can mention it here. One of the reasons we have really focused on character technology is that it touches so many departments and is a very difficult issue to crack, at Crytek we have a strong history of lighting and rendering.

What is ‘Physically-Based’ Shading?

The first time I ever encountered a physically-based pipeline was when working at ILM. The guys had gotten tired of having to create different light setups and materials per shot or per sequence. Moving to a more physically-based shading model would mean that we could not waste so much time re-lighting and tweaking materials, but also get a more natural, better initial result -quicker. [Ben Snow’s 2010 PBR SIGGRAPH Course Slides]


image credit:

A physically based shading model reacts much more like real world light simulation, one of the biggest differences is that the amount of reflected light can never be more than the incoming amount that hit the surface, older lighting models tended to have overly bright and overly broad specular highlights. With the Lambert/Blinn-Phong model it was possible to have many situations where a material emitted more light than it received. An interesting caveat of physically-based shading is that the user no longer has control over the specular response (more under ‘Difficult Transition’ below). Because the way light behaves is much more realistic and natural, materials authored for this shading model work equally well in all lighting environments.

Geek Stuff:‘Energy conservation’ is a term that you might hear often used in conjunction with physically-based lighting, here’s a quote from the SIGGRAPH ’96 course notes that I always thought was a perfect explanation of reflected diffuse and specular energy:

“When light hits an object, the energy is reflected as one of two components; the specular component (the shiny highlight) and the diffuse (the color of the object). The relationship of these two components is what defines what kind of material the object is. These two kinds of energy make up the 100% of light reflected off an object. If 95% of it is diffuse energy, then the remaining 5% is specular energy. When the specularity increases, the diffuse component drops, and vice versa. A ping pong ball is considered to be a very diffuse object, with very little specularity and lots of diffuse, and a mirror is thought of as having a very high specularity, and almost no diffuse.”


It’s important to understand that everything is a hack, whether it’s V-Ray or a game engine, we are just talking about different levels of hackery. Game engines often take the cake for approximations and hacks, one of my guys once said ‘Some people just remove spec maps from their pipeline and all the sudden they’re ‘physically-based”. It’s not just the way our renderers simulate light that is an approximation, but it’s important to remember that we feed the shading model with physically plausible data as well, when you make an asset, you are making a material that is trying to mimic certain physical characteristics.


Once physics get involved, you can cheat much less, and in film we cheeeeeaaat. Big time. Ben Snow, the VFX Supe who ushered in the change to a physically-based pipeline at ILM was quoted in VFXPro as saying: “The move to the new [pipeline] did spark somewhat of a holy war at ILM.” I mentioned before that the artist loses control of the specular response, in general, artists don’t like losing control, or adopting new ways of doing things.


Aside from the more natural lighting and rendering, in an environment where the player determines the camera, and often the lighting, it’s important that materials work under all possible lighting scenarios. As the product Manager of Cinebox, I was constantly having our renderer compared to Mental Ray, PRMAN and others, the team added BRDF support and paved the way for physically-based rendering which we hope to ship in 2013 with Ryse.


General Overview for Artists

At Crytek, we have always added great rendering features, but never really took a hard focus on consistency in shading and lighting. Like ILM in my example above, we often tweaked materials for the lighting environment they were to be placed in.


Before we start talking about the different maps and material properties, you should know that in a physically-based pipeline you will have two slightly different workflows, one for metals, and one for non-metals. This is more about creating materials that have physically plausible values.


  • The specular color for metal should always be above sRGB 180
  • Metal can have colored specular highlights (for gold and copper for example)
  • Metal has a black or very dark diffuse color, because metals absorb all light that enters underneath the surface, they have no ‘diffuse reflection’


  • Non-metal has monochrome/gray specular color. Never use colored specular for anything except certain metals
  • The sRGB color range for most non-metal materials is usually between 40 and 60. It should never be higher than 80/80/80
  • A good clean diffuse map is required



At Crytek, we call the map that determines the roughness the ‘gloss map’, it’s actually the inverse roughness, but we found this easier to author. This is by far one of the most important maps as it determines the size and intensity of specular highlights, but also the contrast of the cube map reflection as you see above.  A good detail normal map can make a surface feel like it has a certain ‘roughness’, but you should start thinking about the gloss map as adding a ‘microscale roughness’. Look above at how as the roughness increases, as does the breadth of the specular highlight. Here is an example from our CryENGINE documentation that was written for Ryse:

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Your diffuse map should be a texture with no lighting information at all. Think a light with a value of ‘100’ shining directly onto a polygon with your texture. There should be no shadow or AO information in your diffuse map. As stated above, a metal should have a completely black diffuse color.

Geek Stuff: Diffuse can also be reffered to as ‘albedo‘, the albedo is the measure of diffuse reflectivity. This term is primarily used to scare artists.


As previously discussed, non-metals should only have monochrome/gray-scale specular color maps. Specular color is a real-world physical value and your map should be basically flat color, you should use existing values and not induce noise or variation, the spec color map is not a place to be artistic, it stores real-world values. You can find many tables online that have plausible color values for specular color, here is an example:

Material sRGB Color Linear (Blend Layer)
Water 38 38 38 0.02
Skin 51 51 51 0.03
Hair 65 65 65 0.05
Plastic / Glass (Low) 53 53 53 0.03
Plastic High 61 61 61 0.05
Glass (High) / Ruby 79 79 79 0.08
Diamond 115 115 115 0.17
Iron 196 199 199 0.57
Copper 250 209 194 N/A
Gold 255 219 145 N/A
Aluminum 245 245 247 0.91
Silver 250 247 242 N/A
If a non-metal material is not in the list, use a value between 45 and 65.

Geek Stuff: SPECULAR IS EVERYWHERE: In 2010, John Hable did a great post showing the specular characteristics of a cotton t-shirt and other materials that you wouldn’t usually consider having specular.


Here you can see the maps that generate this worn, oxidized lion sculpture.


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See above how there are no variations in the specular color map? See how the copper items on the left have a black diffuse texture? Notice there is no variation in the solid colors of the specular color maps.

SETTING UP PHOTOSHOP color_settings In order to create assets properly, we need to set up our content creation software properly, in this case: Photoshop. If you go to Edit>Color Settings… Set the dialog like the above. It’s important that you author textures in sRGB

Geek Stuff: We author in sRGB because it gives us more precision in darker colors, and reduces banding artifacts. The eye has 4.5 million cones that can perceive color, but 90 million rods that perceive luminance changes. Humans are much more perceptive to contrast changes than color changes!

Taking the Leap: Tips for Leads and Directors

New technologies that require paradigm shifts in how people work or how they think about reaching an end artistic result can be difficult to integrate into a pipeline. At Crytek I am the Lead/Director in charge of the team that is making that initial shift to physically-based lighting, I also lead the reference trip, and managed the hardware requests to get key artists on calibrated wide gamut display devices. I am just saying this to put the next items in some kind of context.


It’s very important that your team be able to test their assets in multiple lighting conditions. The easiest route is to make a test level where you can cycle lighting conditions from many different game levels, or sampled lighting from multiple points in the game. The default light in this level should be broad daylight IMO, as it’s the hardest to get right.


I created one of the first example assets for the physically based pipeline. It was a glass inlay table that I had at home, which had wooden, concrete (grout), metal, and multi-colored glass inlay. This asset served as a reference asset for the art team. Try to find an asset that can properly show the guys how to use gloss maps, IMO understanding how roughness effects your asset’s surface characteristics is maybe the biggest challenge when moving to a physically-based pipeline.


As with rolling out any new feature, you should train a few technically-inclined artists to help their peers along. It’s also good to have the artists give feedback to the graphics team as they begin really cutting their teeth on the system. On Ryse, we are doing the above, but also dedicating a single technical artist to helping with environment art-related technology and profiling.


It’s very important to have a ‘cheat sheet’, this is a sheet we created on the Ryse team to allow an artist to use the color picker to sample common ‘plausible’ values.


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We have created a debug view that highlights assets whose specular color was not in a physically-plausible range. We are very in favor of making tools to help people be responsible, and validate/highlight work that is not. We also allowed people to set solid specular values in the shader to limit memory consumption on simple assets.



Above are two things that I actually carry with me everywhere I go. The X-Rite ColorChecker Passport, and the Pantone Huey Pro monitor calibration toolset. Both are very small, and can be carried in a laptop bag. I will go into reference data acquisition in another post. On Ryse we significantly upgraded our reference acquisition pipeline and scanned a lot of objects/surfaces in the field.



Nicolas Shulz has presented many improvements made based on production use at GDC 2014. His slides are here. He details things like the importance of specular filtering on to preserve highlights as objects recede into the distance, and why we decided to couple normals and roughness.

UPDATE: We’ve now shipped Ryse, I have tried to update the post a little.  I was the invited speaker at HPG 2014, where I touched on this topic a bit and can now update this post with some details and images. (Tips for Leads and Directors) Nicolas also spoke at GDC 2014 and I have linked to his slides above. Though this post focuses on environments, in the end, with the amount of armor on characters, the PBR pipeline was really showcased everywhere. Here’s an image of multiple passes of Marius’ final armor:


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posted by Chris at 7:26 PM  

Wednesday, January 9, 2013

Raucous Ball of Noise


I can’t remember the last time I had a new year’s resolution. But this year I decided to go for it.

A friend and I were joking that we increasingly feel like Producers: how we spend a large chunk of our time just making sure that things are moving. That a meeting has action items, or minutes. That tasks are scoped, their dependencies tracked, have resources assigned, or have dates on a calendar. That a process has proper gates to allow for course correction, etc. I now spend a majority of my time writing emails, attending meetings, or talking at desks.

Death by Mail

But what is crippling is the emails. I feel I have made a career out of always trying to be helpful, but I was surprised how easily I reply to anything someone sends me. And how willing people are to just ‘go hunting with a shotgun’ and mail 15 others instead of trying to have a discussion with the right person. Many of the mails I saw myself spending time on were threads involving many people and important topics, I felt the need to be involved, but we rarely seemed to come to solid decisions -just running commentary. These mails often had more than 10 people added in CC ‘for awareness’, but then those people feel the need to contribute their opinion in some way.

It turned the simplest discussion a raucous ball of noise, which often then required the creation of a meeting to make a decision on how to progress.

The meetings were more successful, I think in part to the fact that only the people who needed to be involved in the decision were invited. Unfortunately, I had often spent time on the mail thread to avoid the need for a meeting, only to find myself reiterating my sentiments in a meeting the next day.

I looked for a day where I wrote the least number of mails, the number was ~35, and it was a recent sick day when I had stayed home.

Small Adjustment, Big Victory

So I decided to pull myself out of this, after all it is somewhat self-induced. Of all the options, the best seemed to limit myself to 10 work emails a day. All other communication would be in person, in meetings, or on the phone.

I didn’t think this would have the impact it did.

From this, other things started to fall in place. I really disliked how I would increasingly feel like standard operating procedure was constantly looking for dropped balls. I need to let dependencies and other departments drop their balls, and hope that they will learn from it, or hope that someone else is watching. In essence, trust people more, and as a by product: spend more time being a Director and less a Producer.

10 emails a day forced me to really choose what email discussions I want to be involved with carefully. I was not respecting my own time, and this arbitrary rule forced me to do that. As a result, it allows me to spend more time on Art Technology initiatives, looking at the project, talking with my team, and giving proper direction.

I can’t reject meeting invites, or ignore mails, but this little adjustment has really helped me more than I thought it would.

posted by Chris at 2:42 AM  

Monday, January 7, 2013

Abusing ‘Blind Data’ in Maya

‘Blind data’ is custom data that you can store on any object or its components (vertex, edge, polygon, etc). The documentation says ‘Blind data is information stored with polygons which is not used by Maya in any way..’ I believe it is used when importing meshes from other apps that have properties that do not map to Maya, so that when you take them back to those apps, those properties remain.

Anyway, the important point here is that blind data is metadata (int, float, double, boolean, string, binary) that you can attach to any component. It matters not what happens to said component, you can extract a polygon from a mesh, it’s index will have changed, it’s object will have changed, but its blind data will remain with it. The only drawback can be that it can be painfully slow to write this data, but we will get to that later.

Simple Example

First let’s create a blind data template, this is required to store the data later. We use the command ‘blindDataType’ to create a template for a string type called ‘skinningInfo’ or ‘skin’ for short, giving it an ID 12344. Then we query the ID and it returns the blind data attribs we have created.

cmds.blindDataType(id=12344, dt='string', ldn='skinningInfo', sdn='skin')
print cmds.blindDataType(id=12344, tn=1, q=1)
>>['skinningInfo', 'skin', 'string']

So now we have our template, let’s try using it, this is more focused on getting the idea across than speed:

#query vertex # of mesh
v = cmds.polyEvaluate(node, v=1)
#loop through vertices
for vtx in range(0, v):
    #get influences
    infs = cmds.skinCluster(sc, inf=1, q=1)
    #get weights
    objVtx = node + ".vtx[" + str(vtx) + "]"
    vals = cmds.skinPercent(sc, objVtx, q=1, v=1)
    #build dict of influence:weight
    for i in range(0, len(infs)):
        weightDict[infs[i]] = vals[i]
    #write value to blind data
 cmds.polyBlindData(objVtx, id=12344, at='vertex', ldn='skinningInfo', sd=str(weightDict))

So here you have saved a dictionary per vertex that has key/value pairs of influence/weight. You can query like so:

#I have a vertex selected in component mode
print cmds.polyQueryBlindData(, id=12344, showComp=1)
['polySurface2.vtx[64].skin', "{u'joint2': 0.49755714634259796, 'joint3': 0.49755714634259784, 'joint1': 0.0048857073148042395}"]

Now On To Something More Useful

So let’s create a function to store skinning data per-vertex, as you may have seen with the above, that was painfully slow. If you have written any skinning tools, you know that the solution to this (other than learning C++) is to apply your change to all vertices at once. Below we build two lists, one of vertices and one of weights, then we

def storeBlindSkinning(mesh, sc):
	mesh is a skinned mesh, and sc is the skincluster affecting the mesh
	vtxList = []
	v = cmds.polyEvaluate(mesh, v=1)
	infs = cmds.skinCluster(sc, inf=1, q=1)
	vtxWeights = []
	for vtx in range(0, v):
	    objVtx = mesh + ".vtx[" + str(vtx) + "]"
	    vals = cmds.skinPercent(sc, objVtx, q=1, v=1)
	    for i in range(0, len(infs)):
        	weightDict[infs[i]] = vals[i]
        cmds.polyBlindData(vtxList, id=12344, at='vertex', ldn='skinningInfo', sd=vtxWeights)

Setting all the data at once is 1/3 faster, however, setting this data takes quite some time, and you may want to take a hit for a progress bar. (break it up into groups) On ~60,000 vertices this took 10min (15min doing it inside the loop). I don’t mind that hit if it means that I can now detach/alter/slice my mesh without losing skinning data. You can even extract faces and the new vertices created will get the same blind data as their original. (one becomes two)

As always, the C++ API is much faster, my colleague, Bogdan speed tested the above function and 50,000 vertices took only a few milliseconds, compared to 10 minutes in pythonland.

Remember, there are other ways to store skinning data, using UVs, position, vertex color channels, etc. I just wanted to introduce people to blind data in Maya and show a potential use.

posted by admin at 4:04 AM  

Sunday, January 6, 2013

My 2012 in Review

2012 blew by incredibly fast. If I had to sum the year up into three categories it would be:

  • RYSE / CINEBOX: At Crytek, for the first time ever I broke away from the Crysis franchise and have been working on Ryse with my old friend Hanno Hagedorn, who returned to Crytek this year. In my ‘20% time’ I am still on CINEBOX, which saw some of it’s first production use this year on some high profile film and game projects, but I can’t say much more than that.
  • MAYA: New project, new team, and new software/pipeline! I mentioned this in my SIGGRAPH class, which cleared PR, so no issue mentioning it here: Ryse is the first Maya project at Crytek. In the past year, with the help of Crytek UK, we have been building up a Maya pipeline from scratch. The 3dsMax pipeline was ~10 years old and had a lot of legacy stuff.  Any Maya studio I have worked at always had a legacy pipeline, and I had a mental checklist of things we all would have done differently ‘if we could rewrite everything’. It has been really fun working with the Ryse TechArt team to build this pipeline, we have some really great guys (and gal!), but I won’t out them here. (to the dismay of recruiters everywhere)
  • DIVING: This year I spent a lot more time in the water! Not only diving, but I stepped up my photography; nothing raises your pulse like a changing lenses out over a 200m dropoff! Colleen and I were lucky enough to get to Indonesia, Malaysia, and Egypt. (video, photos) We stayed on an old oil rig off Sipadan where we met a group of great photographers, one of which was Sin Hwa, who took that photo of me above.
posted by admin at 2:27 AM  

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