Map channel (material and UV map / unwrap)
What are map channels ? Usually, when we add a texture and the modifiers UVWmap / Unwrap they come at the default of map channel 1. But an object can have more than one UV; you can add more than one of these modifiers and when set on different channels they do not override each other. All you have to do is keep track of which map channel each texture is using and which modifier is set to that channel.
Back to the material editor. Since we covered most of the process in the material editor, in the next step I'm going to focus mostly on how to work with the UV's. But first, I would like to share how I go about doing most of the tweaking once I've already added some mix levels.
I've noticed that not many people are aware of how useful the "output" tab is. Through the output tab you can easily override and adjust the weight each and every map gets in the mix levels. It allows you to manipulate the colours and sometimes "override" the limit of the contribution a map gives.
I will go quickly through the parameters:
- Output amount - gives control to override the amount of contribution the map will have to the material.
- RGB offset - this basically controls the darker colours of the map. I often give this parameter values below 0 to strengthen the contribution of the darker colours to the material.
- RGB level - this basically controls the brighter colours of the map. I often play with both RGB level and RGB offset - these two parameters can balance each other and the further they are from each other, the more "overridden contrast" the map gets.
- Bump amount - this parameter is very useful to tweak the contribution to the bump for each map. It has effect only in the bump slot, obviously.
- Enable colour map - this one gives a bit further control to most of the things mentioned before, but here you can manipulate the map itself and its colours. It is very useful when you want to use the same bitmap but with some variations - it eliminates the need to create new bitmaps just for that or going to Photoshop just for some basic colour adjustments.
Working with the limits of "show map in viewport"
One last material editor note before we move on. Max is very limited in its ability to show how the maps sit on the model in the viewport - it often doesn't show the correct scale of procedural maps and when several maps are mixed together it can't show the combined end result in the viewport. That is why for the next step you will always need to go to the specific mask you are setting the UVs for and turn "show in viewport" from there. In any case, doing a test render every now and then to see how everything combines on the model is a must to progress correctly.
STEP2- Mixing in details in different map channels and adjusting them on the mesh
Everything done so far can be considered as preparation for this step: this is the main step for this technique.
I've explained how I go about adding more mix levels to the material editor, so now I'm going to focus on what I've done with the UV's for each mix level I've added (Fig.17).
Map channel 1 - blood and general maps
Map channel 1 is the default channel that comes when you work with objects and textures.
That is why I didn't really need to make a new map channel for it - just moving around existing UV's to set where the blood stains fall was enough. I didn't even need to unwrap any model because even if inevitable stretches and overlaps occurred - it didn't really matter too much.
There is a meaning to the order of the mix levels and since the blood will cover the rest of the details, it goes to the base of the maps (Fig.18).