Why?First of all, why? Why create this when there is a perfectly good terrain package that comes with Unity? Well, I do like to have a mess about and find out what I can do, no other reason than that really, why? Because I can :) I dare say that the Unity Terrain asset is a much better way of creating your terrain, having not really played with it I don’t know, but I would like to implement my version of Geo Clip mapping see here:
How?I started off trying to find out if I could generate my own geometry in Unity, and it turns out you can, this was great news on my quest as it meant I can pass my script a height map and using that to generate the mesh needed to render the terrain.
I started off creating a script called TerrainGenerator in my Unity project, in here I added a number of public parameters so they can be set in the editor and I can pass in the height map and the min and max height of my terrain, the txMod is just a variable I can use to modify the texcoords in the vertex, it’s a throw back to the version I did in XNA, and as you can change an assets tiling in the editor, probably not needed now.
Naturally you will need a mesh filter to store the mesh in, if you don’t Unity will throw an error when you go to set the mesh in it. I then check to see if a height map has been given and if not generate a plane and render that instead.
Here is the script in it’s entirety:-
I had a bit of a shock when I first ported this code from XNA, nothing rendered, but I had no errors, then I found out that Unity is left handed, so I just had to reverse the winding order of the index and it worked :) something to be mindful of if you are porting code from XNA.
So, that will generate your mesh AND if you give it a mesh collider, will add it to the Unity Physics system too, it was quite cool to then just add some sphere’s and cubes, give them a rigid body and watch them roll and tumble down the hills :D
So, you can now render the terrain and with a diffuse shader will look something like this:
If you look at the code above, you can see I am setting the vertex colour, I am actually not using this as a colour, but a blend weight used to blend the textures as the height of the terrain alters, my custom shader will now use that value to determine what textures should be used where. Also note that Unity (well there may be a way around this, but I am new to Unity so forgive me) will not render large height maps with this technique, if I go for a big height map texture I get this error:
Mesh.vertices is too large. A mesh may not have more than 65000 vertices.
Custom Terrain ShaderAgain, this was a pretty simple port from my XNA sample to Unity, main issue I had was working out how to extend the vertex structure, but finding you can’t and having to use the Color element of the vertx to store my blend values in. I guess I could calculate them in the shader, but that might be another post ;) Again, the online Unity docs were a massive help with this.
My shader properties are pretty simple, 4 textures along with their bump maps:
To implement it, I created an empty game object, gave it the terrain script, a mesh filter, a mesh renderer and a mesh collider, I then changed the shader to be my custom\terrainshader set the params on script and shader as I wanted.
There are a few other bits and bobs in there to iron out and polish, but think I am now ready to move on to that geo clip map implementation :) I hope it’s going to be as easy as I think it will be….
Here is my shader in full
The discovery of the class attribute [ExecuteInEditMode] means that my height map terrain can now be viewed in the editor too :D Awesome !!