When needing to apply decals, use the ‘Composite’ map. This is an extremely powerful map type that allows you to easily and precisely place graffiti on walls or product labels to bottles.
The workflow is simple, and shown below:
1. In the Slate material editor, add a ‘Composite’ Map into the diffuse socket/channel of your material, as below.
2. Navigate to the ‘parameters’ section of the material editor (or press P to toggle on/off)
3. In this parameter interface we have a number of options that we can investigate.
A. In particular note, the opacity weighting of the map:
B. Photoshop style blending modes.
C. Layer duplication, blending, and renaming options.
D. The 2x ‘color correct’ map options, embedded into this map type.
4. Now add a secondary layer. This is similar to an Adobe Photoshop workflow, where it draws from the bottom of the stack upwards. Therefore if we were doing a brick wall with graffiti, then the graffiti would need to be on the top layer with a mask, and the bricks underneath.
(Ensure you rename the layer using the options mentioned above.)
5. From here we need to plug individual bitmaps into the texture or mask sockets. (This mask option works in the same way an opacity map works.)
The Texture channel input is:
The Mask channel input is:
6. Add your bitmaps, or procedural textures to the relevant inputs (or sockets). Below is an example of what I quickly chose.
In the above example you can see that I have also enabled the maps within the viewport to allow me to get immediate feedback on their placement, without the need for test rendering. To do this right click on the materials header and choose ‘Show Realistic Material in Viewport.’ (The visual Red and blue split within the material header indicates its enabled)
7. Reorder the layers, so the layer order works for your bitmaps as described in point four. This is accomplished by dragging the layers header to the required new positioning.
8. You should now have something in the viewport that looks this (but probably looks a lot better!)
9. The same rules of texture co-ordinates apply to these maps, as normal bitmaps etc. So ensure they are adhered to. Luckily we can start to mix the UV co-ordinates though, by using the below options within a ‘UVW Map’ modifier and the bitmaps options. This allows for greater control.
This is an overlooked map type, and one that you should investigate. Its also worth mentioning that if you go crazy with a vast amount of layers, then you will experience an expected performance slow down. That said I have never needed more than 6 composite layers. When working in Photoshop I will easily have 100 layers.