Blend mapping is one of the key features in Cryengine3. With blend mapping you are able to blend two different textures. It is very useful to break up the repeating when you're using two tileable textures. It can also serve to give localized dirt, wear, tear, etc.
Once the basics on how blend mapping works the use can be limitless and give the artist a lot of freedom to make a great looking asset spectacular with little use of resources.
In the following tutorial we will explain the basics of blend mapping and what to look out for when using it.
We will be blending these two textures on a flat plane.
The first thing we need to do before we can blend map is prepare our geometry correctly. One caveat of blend mapping is that is it tied to our vertices in the geometry. That means that we have to add more geometry in places we wouldn't usually. It also means that we need to model very clean and neat as the more even the subdivisions the better result we'll be able to achieve when blend mapping. Also the more subdivisions we add the more accurate well be able to tell where to blend and where not.
In modern game development geometry is a little bit cheaper than using lots of textures. As long as we keep our vertices count reasonable it should be ok.
Down below we created a poly plane with subdivisions.
To control the blend and where it's going to show on our asset we need to paint our Vertex Alpha. The range in our spectrum is 0-255, with 0 being black and 255 being white.
If the vertex alpha is 255 (pure white) on our asset it means that only the original texture will show up. On the other end of the spectrum if the value on the vertex alpha is 0 (pure black) the blend will show up.
Since we have a range from 0 to 255, we can use the full spectrum and decide how much and where we want the blend to show through.
To further break up the tiling and have even more control on how our textures are going to blend we have the blend mask. The blend mask acts like an alpha. With that we can have parts our original texture show through even if we have that part of our vertex alpha on the geometry painted black.
Since our blend mask acts like an alpha all the white parts will be displaying our blend texture all the black parts will displaying the original texture.
As you can see down below we have taken the brick pattern and added some noise. We also, in order to increase believability, made the grout in some places black, so the original grout from the bricks will show through.
Once you have your textures, it's time to bring the asset into CRYENGINE. After the asset is in the engine and the shader assigned, we need to activate the blend layer.
In order to do that we open the tab in the Material editor named "Shader Generation Params". There we click on the checkbox "Blendlayer". After clicking on that you'll notice that new slots have become available.
The extra slots are named:
In those we'll load in our blend textures. One good tip is to load the same normal map from the original texture, this way it will give the blend texture the brick pattern.
This is on a case to case basis, but if you're doing dirt, paint, etc. which doesn't have a unique surface property it is a good idea to reuse the same normal map.
The blend has two settings that need to be tweaked to give a good result. You can find those in the "Shader Params".
They are as followed:
By tweaking the Blend Factor we can adjust how much of the blend texture gets blended in. In other words it acts as an opacity slider in Photoshop.
By tweaking the Blend Falloff we can adjust how harsh the between the blend texture and the original texture is.
In other terms we are adjusting the feathering of the blend mask. This means the higher the value the softer our alpha gets (which in this case is the blend mask).
Once you have everything tweaked you should get a result like this:
As you can see the bottom right corner is completely free of the blend, since this is the part that we left white and only the original texture is coming through.
You can also see as opposing the bottom left corner is fully blended. But you can also see that the grout is the original one coming through, since our blend mask we left that black.