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Read the article or watch the movie. Both contain (almost) the same content.

I didn’t embed the video directly to avoid any tracking from Google and complications with the DSGVO.

Grand Theft Auto V has some nice fountains which I would like to present you – but sometimes it’s a bit hard to admire them in the game :,(

Source: GTA V

It can be equally hard to put nice water effects into a game. One reason for this is, that water has an always-changing surface-topology.

While the polycount for e.g. a cloth-simulation stays consistent (and the vertices “just” need to be moved around) every frame of a water-simulation has a different amount of polygons/vertices:

Blender Cloth/Liquid Topology Example

It’s possible to use newer techniques like Vertex Animation Textures or “Geometry Flipbooks” á la Alembic but what I saw in GTA was simpler – that’s why I would like to show it to you.

Here is the first one. As it looks a bit like a worm, let’s call it:

Wormy Fountain

Source: GTA V

In case you think: “Well … that’s water, so what?” I would like to underline, that having a nice volume and/or silhouette for the water is not that easy – and in the example above we have a both! <3 :)

To illustrate the problem: For water-effects often a water-texture is moved along a flat surface which sometimes works very well. Here, is a great example which we shall name:

Wedding Cake Fountain

Source: GTA V

But if try to mimic the “Wormy Fountain” by running a texture along a static geometry (like it was done for the “Wedding Cake Fountain”), the trick gets very obvious when looking at it from the side:

Of course, you could use a geometry with some volume instead of a flat plane. Luckily, GTA offers an example for that as well. I’m introducing to you – last but not least:

Tongue Fountain

Source: GTA V

Here we have a geometry which some volume which works perfectly fine from any angle but there is a “but”.

Source: GTA V

Here comes the “but”.

But the silhouette is very static and not as dynamic as we saw it on the “Wormy Fountain”. Let’s look at the effect again:

Source: GTA V

Looks very good from all angles and has a nice dynamic silhouette, doesn’t it?

The Secret

The secret behind this water-stream is called: Spline with camera-facing quads.

Source: GTA V

The polygon-ribbon is re-orienting itself toward the camera and with that you’ll never see, that it’s actually a flat polygon-stripe. Only when you look at it from very extreme angles, you might see some artifacts:

Source: GTA V

You may have seen similar techniques in other areas for example on the Home World Trails or from the Company of Heroes flame thrower (see image below), but I thought making a fountain with that is very creative so I had to share it with you guys. :)

By the way #1

Here is the texture which was used in GTA:

Source: GTA V

By the way #2

I have no idea what these smaller geometries are for … they are not visible in the game:

Source: GTA V

By the way #3

This effect inspired me (together with other influences like this great talk about loopable liquids in Mortal Kombatcareful, the talk also features many blood effects!) an idea in my mind: If a simple moving texture on a polygon-trail/spline already looks so nice, could this work even better with a tileable mesh moving along a spline?

To test this, I made a small side-project:

It uses two tileable meshes (generated in Houdini) and 5 instances of each run along a spline. If you want to see the full breakdown, I put everything together on my Artstation post.

Thanks for reading my article. <3
I hope you’ll like it!

And never forget:

Source: Giphy
Update 1

Smou and DrWDSo told me that there is actually a name for the “water without turbulence” I was so amazed by (you can see it in the youtube video I recorded): “Laminar Flow”. And both linked me to this amazing video you should watch. Right. Now! :)

I didn’t embed the video directly to avoid any tracking from Google and complications with the DSGVO.

Update 2

Wyvery and Luos just mentioned that it’s not really a trail but more a spline with camera-facing quads. Thank you for the hint! :)

In Unreal there is a “Spline Thicken”-Node to use this technique e.g. for cables but Luos also told me that he likes to use it for his soul coasters.

Update 3

Geoff Lester created a very interesting blog post after talking with Martin Kepplinger about the question: “Is it possible to make a Particlesystem loop in Houdini?”.

Update 4

Bananaft sent us a small video showing a guy who suddenly loses a big red sausage. This sausage is actually a trail-geometry between particles and those particles can collide with the level geometry. Another very creative use for those kind of geometries. :)

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