Skinning Assetto Corsa Cars from Nothing using Mudbox and Photoshop

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
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.
tW27zHe.png


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.
    PFRDqcNl.png

  2. Hide everything in the Object List
    vK0Fq6Cl.png

  3. Show only Geometry
    DWA09AHl.png

  4. Switch to Object Selection, and turn on Mirror on the X axis.
    O9lP6tQl.png

  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:

cNmg23N.png


...continued next post...
 
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I was using a tablet a bit in the very beginning when I was doing a lot of "art car" type designs where a freehand drawing would the order of the day, but 99% of my stuff now leverages stencils, so there's no real reason to dust off my tablet when adjusting position and rotation of stencils is just as easy with a mouse.

If I DO need to "draw" something, the Steady Brush option in Mudbox helps quite a bit to keep the lines clean. But I've gotten so comfy with stencils that I can usually make any clean shape I want with just a few clicks.
 
Yeah, quite a few textures are going to be tiled on the UV mapping which drastically saves texture size on a lot of cars. In the case of that car I'm guessing that the author wanted to easily have dozens of colors available which would only require you to change like a 16x16 texture.
 
Does anyone else have a issue with like a ghost image in photoshop.
If I use brush in mudbox to make a rough shape then use a stencil to refine the shape all looks fine in mudbox I export to photoshop and it shows the shapes I've made all fine but if I use the wand tool in photoshop it will pick up all the rough shape that I made in mudbox and not the clean shape?.

Only way I seem to get around this is when refining shapes in mudbox when I erase I have to make multiple passes over what I want to delete my erase is on max strength not sure if there is anything else I can try?.
 
I will try and explain issues with a few pictures wondering I'd anyone else has had something

In this picture I have just used brush and made a rough shape.

FB_IMG_1615255734715.jpg


Then export to photoshop and if I select with wand all ok as can be seen

FB_IMG_1615255741680.jpg


If I then define shape in mudbox with stencil and eraser tool looks fine in mudbox

FB_IMG_1615255747542.jpg


If I then export to photoshop and select with wand as you can see it still picks up the original shape even though its not there?

FB_IMG_1615255754963.jpg


If i go over the shape with multiple strokes with the eraser in mudbox and this is set to highest strength then export to photoshop and then use wand as you can see the shape is perfect.
I cannot see why it will not delete fully on first pass over.
Any ideas or things to try would be fantastic as its very frustrating when im trying to refine shapes in photoshop.

FB_IMG_1615255759999.jpg


I have tried different fall off settings turned pen strength on and off tried with snap on and off. Not sure if anyone else has experienced a similar thing and if so what they did.

Thanks

Justin
 
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Yeah, I've encountered this a number of times... sadly I can never remember the way that I eventually get the wand tool to select the correct thing. MAYBE this was the solution that worked? It isn't perfect, but it's a start: Hide all other layers and export the entire file as a PNG and then bring that PNG back as a layer into the original file.

My PC setups are still getting sorted out post-Texas Snowmeggedon, so I can't even open up a file to look at it. Good luck!
 
I will try and explain issues with a few pictures wondering I'd anyone else has had something

In this picture I have just used brush and made a rough shape.

View attachment 452923

Then export to photoshop and if I select with wand all ok as can be seen

View attachment 452924

If I then define shape in mudbox with stencil and eraser tool looks fine in mudbox

View attachment 452925

If I then export to photoshop and select with wand as you can see it still picks up the original shape even though its not there?

View attachment 452926

If i go over the shape with multiple strokes with the eraser in mudbox and this is set to highest strength then export to photoshop and then use wand as you can see the shape is perfect.
I cannot see why it will not delete fully on first pass over.
Any ideas or things to try would be fantastic as its very frustrating when im trying to refine shapes in photoshop.

View attachment 452927

I have tried different fall off settings turned pen strength on and off tried with snap on and off. Not sure if anyone else has experienced a similar thing and if so what they did.

Never happened to me with mudbox, but usually I don't go back anyway after painting.

In photoshop just use different match method, maybe transparency or less tolerance when selecting colour.
 
I will try and explain issues with a few pictures wondering I'd anyone else has had something

In this picture I have just used brush and made a rough shape.

View attachment 452923

Then export to photoshop and if I select with wand all ok as can be seen

View attachment 452924

If I then define shape in mudbox with stencil and eraser tool looks fine in mudbox

View attachment 452925

If I then export to photoshop and select with wand as you can see it still picks up the original shape even though its not there?

View attachment 452926

If i go over the shape with multiple strokes with the eraser in mudbox and this is set to highest strength then export to photoshop and then use wand as you can see the shape is perfect.
I cannot see why it will not delete fully on first pass over.
Any ideas or things to try would be fantastic as its very frustrating when im trying to refine shapes in photoshop.

View attachment 452927

I have tried different fall off settings turned pen strength on and off tried with snap on and off. Not sure if anyone else has experienced a similar thing and if so what they did.

Thanks

Justin


are you doing some ACC skins ?
 
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