Technique for Automatic Lava Flow?

[Deathrey (DeathreyCG)]

@mariomguy;572879

This already works way better than the world projection methods I tried! Thank you!

The problem with world projection is not what happens around UV seams, but how the texture is mapped at the top and around the sides. You can get a decent cylinder by blending two different sides, but the top surface will not flow downwards because it is inherently locked by planar map from the top down. I used world position to make a mountainous landscape and fixed this issue by using a horizontally-emphasized texture for wrapping around and a neutral base texture for the top while lerping the normals from the side so the top is always plain (to make sure the top normals don’t interfere with the side ones). Obviously this solution makes rocky surfaces look smooth, but given a certain style it actually looks quite lovely. And this method has its own issues with seams popping up for seemingly no reason in certain places, most likely a flaw with the way world aligned normals are calculated because the textures have no glaring seams at all whatsoever.

This method is the ONLY one I know of where lava will always flow down. And it only looks wrong on UV seams. I’ll try this on a mesh without any UVs set up.

Just so you know, the UDK rain example does calculate flow in all directions, it just doesn’t shift the top too much. But my biggest problem with that is the flow is calculated in screen space, so when you make the effect larger and more deliberate and move around the screen, it looks very weird.

I assume we are speaking about this UDK mat:

https://udn.epicgames.com/Three/rsrc/Three/MaterialExamples/ex_wet_full.jpg

If that is the case, there is no flow calculation. For RB and GB projections, B is being incremented by 0.25RainSpeed, while R and G are shifted by 0.01RaindSpeed. So thats… not really down. It is close to vertical, but only in projection space. RG projection is simply being panned by 0.01*RainSpeed, just so that it does not appear being still.
This way it is relatively cheap, and it is hard to note the actual direction of the water. Fake, but cheap and efficient. That will be not as cool for lava.

That is why I imply on possibility of calculating actual flow direction, based on relation of vertex normal or explicit normal to world down vector. You would follow the same logic, as calculating it in tangent space, but do it for projection space instead. I will try to sketch a quick MF example, if I have some time later today or tomorrow.