Basic Parameters

• Tiling mode:
  Determines whether to tile beyond the handles in the 2D view. 
  H stands for Horizontal, while V stands for Vertical.
• Bottom Material Color Match: 0-1
  Adjust the colors of the decal material to match the color value of the layers below it.
• Normal Blending mode:
  Adjust how normals are blended between the decal material and the underlying layers
• Normal Opacity Blend: 0-1
  Change the opacity of the decal material's normals
• Decal Height Position: 0-1
  Adjust the height of the decal relative to the underlying layers height
• Decal Height Scale: 0-1
  Change the contrast of the height map for the decal material

Advanced Parameters

• Decal Transformation: 
  Adjust the matrix transform values for the decal. In general it is easier to just use the handles in the 2D view to adjust the decal's transform.
• Decal Offset: -1 to 1
  Adjust the offset of the decal.

To use the Decal filter:

1. Add the Decal filter to your layer stack
2. Under the Decal layer, an Input slot will appear
3. Drag your decal material into the Decal layer's input slot

You can adjust the filter parameters in the Properties panel by selecting the Decal layer.

You can adjust the parameters of the decal input material in the Properties panel by selecting the material in the input slot.