Skinning Assetto Corsa Cars from Nothing using Mudbox and Photoshop

[Russell Sobie]

This Tutorial was originally posted over on the simracingsystem.com forums where I do all of my skinning. I was constructing it AS I was learning the process, so obviously some of this is going to be "not the best way" to do certain things. I was going to make a post just linking the original tutorial, but after asking permission to the folks here at RD, it was suggested that I just post the tutorial in its entirety here! That said, let's get started!

NOTE: I have added notices before or during the parts where it is SRS specific, like making sure your skin is under 10MB (a limitation of the SRS Skin Transfer App used to automatically share custom skins just before races start). Follow the red instructions so you aren't doing extra work where you don't need to!

Software Used

• Adobe Photoshop (with NVidia Texture Tools for Photoshop Installed) (or... with Intel Graphics' version of a similar Plugin that works better for more recent versions of PS)
• Autodesk Mudbox
• kn5conv.exe
• Content Manager
• Notepad++
• Greenshot

The Goal
Since it is almost the end of the current season and I don't know what cars are going to be used next season, I figured I'd learn on something that I figure will EVENTUALLY come up. So the McLaren 650 GT3 is what I'll be doing. The goal is to replicate my typical Red/Black two tone design, complete with a skull on the hood using the most efficient means... rather than just fumbling around with a wireframe texture in Photoshop like I have been doing.

Disclaimers

• I'm not a professional artist. I have a background in graphic design and some 3d modeling but make no claims to know the best way to do any of this stuff. This is just what I've learned jumping in head first.
• Also, Mudbox crashes. A lot. Save often!

Extracting 3D Model
I started by using a program called 3DSimED3. Unfortunately it only has a 20 day trial, and today it ran out. Normally in this situation I would just purchase a licence and call it a day, but I was curious if there was a better way to just get a 3D model out of the .kn5 files that Kunos includes in a normal installation of Assetto Corsa. My googling lead me to this youtube video: Assetto Corsa KN5 Converter & Download

I was unable to find the origin of kn5conv.exe, but I ran a few scans on it and it turned up nothing, so I gave it a try. Works great. Here's how _I_ would recommend extracting the model (as opposed to how the youtuber above does it):

1. Create a Workspace for your new skin outside of your Assetto Corsa file structure. Here's mine: S:\GameFiles\AssettoCorsaStuff\cars\ks_mclaren_650_gt3\workspace
2. Copy the mclaren_650_gt3.kn5 file from your Assetto Corsa installation into this folder (you can find it here: ...\Steam\steamapps\common\assettocorsa\content\cars\ks_mclaren_650_gt3.kn5)
3. Place an instance of kn5conv.exe in your workspace folder.
4. Drag the KN5 file onto kn5conv.exe and watch the magic happen.

The result is that in your workspace folder you will now have a number of file types that can be understood by a number of 3D software packages, such as Mudbox and Blender. I gave Blender my best shot, but couldn't figure it out and there was not a good tutorial I could find that would clue me into how it works. I did find one that was enough help so that I could get going in Mudbox, so that's what I'll be doing.

If interested, here's the youtube video I found that got me going:

Cleaning Model For Painting
Once you have an .FBX file for the car you want to paint, you can import it into Mudbox.

1. Open Mudbox.
2. File>Import...
3. Navigate to your workspace folder and import mclaren_650_gt3.fbx
4. Save the scene as a .mud file (mclaren_650_gt3.mud) in your workspace folder.

This is ALL of the geometry and a bunch of other nodes/objects that you will not need for the purposes of creating a livery. So we must now delete all of the stuff we don't care about. This will speed up performance within Mudbox, as well as avoid Mudbox wanting you to add additional materials every time you attempt to paint on a different mesh. In other words, we want to avoid painting on the windshield when what we want to do is paint on the car's body. Here's what I did to go through everything:

1. Change to the Object List.
   
   
   
   
2. Hide everything in the Object List
   
   
   
   
3. Show only Geometry
   
   
   
   
4. Switch to Object Selection, and turn on Mirror on the X axis.
   
   
   
   
5. Select geometry in the scene view that you know you will not be painting. Windows, tires, brake discs, windshield wipers, whatever. All that should be left are the panels of the car you want to put your design on.
6. Save your .mud file. You may want to save it as a different .mud file than the original, in case you realize later you deleted some part of the geometry you actually wanted!

The end result should look a bit like this:

...continued next post...

 

[Juttie205]

I have tried it and have managed to export picture which is fine then I've just drawn a shape which was fine then I sent it back to mudbox and it paints it straight to car and not like your video where it is like a template and not sure why your car goes pink what stage have I missed many thanks

 

[Russell Sobie]

The first thing... I forgot how to do. I never had very good luck with it so that video in particular was a big test of the workflow. I found I just more enjoy adding/subtracting with stencils. I recommend searching for Mudbox tutorials for how to bounce back and forth between Mudbox and Photoshop.

For the part about the ghosting stuff... if I understand you correctly, I've run into that recently myself. I think that's just a bug on Mudbox's side. The workaround I've done is inside Photoshop, do a Wand Selection of everything not painted, and then delete. If the layer seems translucent, deselect everything, lock transparency in the Photoshop Layer, then color over what is left so it is opaque. Once that's done, re-import to Mudbox, which should get rid of all the invisible nonsense.

 

[Juttie205]

Thanks i was doing something similar with wand tool but inverting selections and deleting will try your way

 

[Juttie205]

Hi russel

I was wondering if you could help i have a fbx file that seems to be very weird in mudbox that when I go to paint it just paints in patches and will not allow them to be painted could i send you the file and you have a look?

 

[Russell Sobie]

Host it somewhere and I'll see what I can do.

 

[Juttie205]

What do you have access to i can put on my mega file tomorrow and post link here?

 

[Juttie205]

here you go Russell many thanks

78.48 MB folder on MEGA

103 files

mega.nz

 

[Russell Sobie]

This thing crashes Mudbox when I zoom in close enough to it to do anything. Also, it looks like this is an older version of this mod? https://www.racedepartment.com/downloads/mini-cooper-jcw-uk-challenge-f56.30469/

I was able to skin the latest version without issue using Mudbox, as you can see here:



If I'm mistaken and this is some other version of the Mini... then I don't know what to tell you. Maybe that version of the car just has too many issues for Mudbox to handle?

 

[Juttie205]

Thanks will take a look at your link

 

[Juttie205]

Many thanks for taking a look at it don't suppose you could do a guide how you used the 2d template in your peugeot 106 video as looked very handy.

 

[Juttie205]

Also just downloaded the mini seems better but each part seems to have a different material like if I paint main body then try and do arches they seem to be seperate is there a way of making all parts so can be painted on with multiple layers. As it seems I have to paint body and export to photoshop same with arches etc,bonnet vents is not come accross this before so was wondering if there is a way to group all together sa can be painted as 1

 

[Russell Sobie]

Once I delete all the objects I know I'm not going to paint (which is typically every object that isn't mapped to the main skin texture), I assign all of the remaining objects to the same material in MudBox, and delete the unused materials. This ONLY works if you know everything that is left is mapped to the same texture... otherwise you are going to paint on stuff and it'll overlap with something else and it'll be a mess.

As for the 2D "template" I posted a reply as a comment, but here it is here:

This isn't exact, but this should probably get you 90% there:

1. Once you have your car's mesh trimmed down to just what you want to paint...
2. Create a Plane in your scene.
3. Translate and rotate and scale the plane so it is out of the way.
4. Apply the same shader to the Plane that is on the rest of your car.
5. Profit!

 

[Juttie205]

Ok will take a look seems alot of work for the mini never had these issues on other cars

 

[Juttie205]

Think ive made a right hash up of it my wireframe has gone mad and paint goes everywhere now.
Don't suppose you could sort all paintable parts and send to me would be really appreciated as think I'm getting in a complete muddle here

 

[Juttie205]

I have just tried to do bumpers and assigned existing material body to it them deleted the bumper materials but when i go to paint its over lapping and when i export to ps it shows wireframe for arches and bumpers on top of body mesh??

 

[Russell Sobie]

Yeah, sorry... I don't really want to be the Mudbox AC Livery Hack Workflow IT guy on the Internet.

That said, what I see is you painting on parts of the car that are mapped to different end textures. You need to combine only the objects in Mudbox to the same material when you have confirmed that they are, in fact, going to be mapped to the same diffuse texture.

Just kind of guessing looking at your image above, it looks like there's probably a "plastic" or "carbon" diffuse texture that is separate from the "body" diffuse texture. You should either lock those objects while you are painting the body, or simply delete them from the list of objects in Mudbox and just use the default plastics and carbons.

Put another way: You can use Content Manager's CM Showroom by clicking on the different body parts and looking at the txDiffuse assignment to see which diffuse texture it's going to be mapped to. Figure out which ones are the "body" texture, and only keep those available for painting in Mudbox.

 

[Juttie205]

ok i have been playing around and getting somewhere slowly and you right about arches etc being plastic and have noticed on all the other skins in game these have a separate wireframe etc.
When I select on main body my layers say Body and i paint then when i click the plastic parts the layer section changes to arches which I'm guessing means its painting on them separately.
What is the best way to swap between these as at moment i have to click on car model also when I export to photoshop i right click on body and export then i have to click on plastic parts and export this then shows to seperate wire frames in photoshop and thats the same as all the other skins in game/ is there a way when i export to photoshop it will send over everything together and just open on 2 pages in photoshop. hope this make sense.

 

[Russell Sobie]

Somewhat, yes. Basically if you are going to paint on two or more materials at a time, you'll have to export each material's paint layers separately (two different exports to PSDs). This is usually a pain in the ass, so typically I will either just delete or lock the parts of the mesh for the non-body parts in Mudbox and simply not bother with them.

In the rare case where I DO actually want to paint on 2+ materials at a time, I have to be very careful about the layer names so I can switch ALL of the current layers on all the materials. So many mistakes of me painting over something and it painting in a layer I don't want to touch yet. Typically I'll lock one set so my paintbrush won't actually paint on faces for the other materials, and then once I'm done with the main body, lock the OTHER set of objects and do the other material.

I'm just reading what I just wrote above, and frankly it's a confusing mess unless you are fairly familiar with 3D applications that have materials and textures and UV mapping, etc.. I'm pretty familiar with them at this point and the above confuses ME. Best of luck!

 

[Juttie205]

Thanks I've sort of got my head around it last night just a pain I have to export them separate but not end of world.
Is there a shortcut to switch between materials layers or is it just matter of clicking on that part of car to change the layer box.

 

[Russell Sobie]

There probably is a way to cycle through the different materials, but I don't know what it is. I usually just click on it with the Brush tool (and if I accidentally paint something, just do an undo). Actually that's not true: USUALLY I delete stuff that isn't body paint and not bother with secondary stuff unless the car really, REALLY needs that work done.