Texturing the mesh in Substance 3D Painter

Prerequisites
Configuring Substance Painter
Modeling the mesh in Blender

General texturing

1. Open a new project
   1. Select 4K textures
   2. Select the Kerbal_Space_Program_2_Parts_Paintable template.
   3. Import the FBX
2. Find the KSP2_Part Smart Material and apply it to the mesh.
3. For some reason doing this will bring in some stuff already on the Edges layer that applies to the Heightmap (thus the orange bar under it). You should clear the black mask on Edges to get rid of those. Just right click on the black mask and select Clear Mask.
4. You can drop any materials (smart or otherwise) into the Base Material folder inside the KSP2_Part folder. These are what you use for most details, with the exceptions being some things you'll do on Nails, or Edges, or Emissivity. Since applying the KSP2 smart material to the whole thing includes applying a KSP2 Steel material without a mask inside the Base Material folder, everything will start out as a shiny steel. I leave this as the last layer in that stack to catch anything I don't otherwise paint, and put other painting layers above it with masks.
5. For paint map, just open up the PaintMap folder and apply whatever strength you need to the black masks for Base and Accent. This works just like painting on any other black mask. Mostly, you'll just apply full strength to indicate (yes, please apply the player's base or accent paint color here). Using anything less would result in the player's attempt to paint the part being diluted. You need to paint Base everywhere you want any color (accent or base), and then also paint Accent where you want the accent paint to be applied. If there is no base paint somewhere, then whatever you paint in Substance Painter will be what the player gets and they can't change it.

Did you know?

The height channel induces a real deformation of the mesh (works well with a lot of polygons) while the normal channel is a bumb map.

Substance 3D Painter converts Roughness to Glossiness automatically. The export template uses the Glossiness channel.

Creating gradients

1. You must bake at some point before this, and your bake must include Position as we'll need that. If you've already baked your model in SP, you don't need to do it again.
2. Starting with an Emissive layer (you can have more than one if you need more than one color - just duplicate and customize), paint at full strength (1.0) on the black mask everywhere you want the gradient to be.
3. Right Click the black mask and pick the add generator option.
4. Click on the resulting Generator (no generator selected) button, and pick the second option from the left for 3D Linear Gradient.
5. The Image inputs should default to Position, so just switch your display from Material or whatever to Position and orient your part so you can see the point where you want the 0 for the gradient to be like this (the display picker is in the upper right corner of the panel with your 3D view).
6. Take the eye dropper from the 3D Position End and click on the place you want the End to be. This assumes that the Start is already where you want one endpoint of the gradiant to be, as it is in the view above. If you oriented your model so that the End is already where you want it, then use the other eye dropper and set the start. The objective is that you've got the Position mapped colors pinning down the range across which you want the gradient to go. Don't worry if Start and End are reversed from what you want because...
7. Set Invert to be True if the gradient is going the wrong way! (as it is in the example above).
8. Most Important! Set the generator to apply as Multiply (it will default to Normal). This is the part where the work done on Step 2 will help you as it will then correctly constrain where the gradient is applied.
9. When you're all done, you can set your display to Mask so you can see how the gradient will be applied to whatever color you set for your Emissive. BTW, there's nothing magical or special about the name for the layer. If you chance it to Engine Glow or Emissive 1 or whatever it will still add to the emissive *_e.png texture as that is how the Emissive layer was setup when you applied the KSP2 Smart Material.

Exporting the textures

1. Press Ctrl+Shift+E to open the export window.
2. Select the Kerbal_Space_program_2_Parts_Paintable output template.

Useful links
Substance 3D Painter tutorial: https://www.youtube.com/watch?v=_j27AS0VQOw
Free materials: https://substance3d.adobe.com/community-assets/
Paid materials: https://www.artstation.com/
Lux's notes on Paint Map: https://luxstice.notion.site/How-to-create-a-paintmap-texture-59c51441f4d048a5803c0b2b108cd041