To only see the vertex alpha in the viewport, right click on your object, check Vertex Channel Display, and set it to VertexAlpha.
Setup in XSI
- Model and texture your object normally with standard materials and a diffuse texture.
- Select your object and from Render toolbar choose Get – Property – Color at Vertices Map.
- Then you have to go to Camera Display Property Editor and set Vertex Color Property Display to Show Alpha.
- Press Ctrl+W to open Brush Properties property editor and set the Color Paint Mode to Alpha.
- To set the Alpha value, you must use the A slider in the palette controls' RGBA sliders.
- Where your object has transparent vertices, there the dirt layer will be visible.
- Export your object to CryENGINE.
- Set up dirt layer materials in CryENGINE.
Usage in CryENGINE
The dirt layer currently only works with the Illum shader. First load up your Dirt Texture in the Custom Slot of the shader. Then check Dirtlayer under Shader Generation Params to enable the Dirt layer parameters.