Research Project: A Break Down on how to use Vertex painting

 What is Vertex Painting? 

Vertex Painting is a process used in order to paint texture maps onto vertices. It is a useful setup to have when you need variation in your environment. It breaks up the continuity you may have when doing repeatable textures, such as a brick wall. 

It does this without needing extra work creating a bunch of individual texture maps that are unique and different. Instead, you are the one using vertices to paint on a texture, almost like adding a new Photoshop layer, right in engine! 

The setup is rather simple to pull off for a basic Vertex Paint material. I will break it down into sizeable steps to follow in order to create your own. 

Step 1 

You need at least two types of textures! One should be the "base" texture and the other should be the "modified" texture. For my example, I used one 'clean' wall and one 'dirty' wall as shown below. The only difference between the two is one has dirt I want to paint onto the mesh vertex, and the other one does not. 

Step 2

After your textures are properly imported into unreal engine, it is time to make the material with the Vertex color information. Fortunately, Unreal Engine makes it really easy to set up. 

1. Create a new material 

2. Create a Lerp (LinearInterpolate) node. 

3. Add a vertex color node 

4. Plug the dirty texture that you want to paint into the 'A' slot of the Lerp node, the clean texture into the 'B' slot of the lerp node, and then the vertex color node into the 'Alpha' slot of the Lerp node. Plug the lerp node into the Base color node. Your setup should look something like so: 

Step 3

With that setup established, you are ready to start painting. Save your material and exit back to the viewport. In order to do Vertex Painting, Unreal has a feature called 'Mesh Paint Mode.' Switching Modes can be done on the top left of the viewport: 

The Vertex painting tool makes it easy to paint in your details. It uses color channels in order to do so. The color channels on a generic RGB is split up into Red, Green, and Blue channels. So, hooking up the 'Red' channel like in the setup described in step 2 means that we are painting on the texture map with the 'red' channel. You can check the 'red' channel option here: 

Here is a visual explanation on how the RGB channel functionality is working in viewport: 

A note that sometimes it can get a little finnicky. I have the Paint color set to black, the erase color set to white, and the brush strength set to 1. 

You can play around with some of the other features, such as the brush size, the fill feature, and the clear feature. 

Step 4: Taking things a step further 

Okay, so there is a way as to paint in a single texture on top of another. But what if I want to have multiple textures onto different channels and switch between them? That is totally possible to do. I was able to accomplish this with this setup right here: 

Instead of plugging the red channel of the vertex color into each lerp node, I instead used the Blue and green to my advantage as well.  These textures all lerped together gave texture information onto all three of the Red, Green, and blue channels. In order to paint the texture of my choice, I simply checked the color of the channel box that I wish to paint. You can select multiple and paint all three at once if you are chaotic enough, or you can simply use them one at a time- all using the same material. 

Happy painting!