You can choose!
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. :)

2 thoughts on “GTA V – The Wormy Fountain

  1. E. Bicalho

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

    You forgot the last video, “Update 1”.

    Reply

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