GTA V - The Wormy Fountain, Hacker News

You can choose!

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

I did not 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:, (

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:

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 !

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:

But if try to mimic the

“Wormy Fountain”

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:

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

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:

Looks very good from all angles and has a nice dynamic silhouette, does it ?

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

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:

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. 🙂

Here is the texture which was used in GTA:

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

This effect inspired me (together with other influences like this great talk about loopable liquids in Mortal Combat – careful , 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.

And never forget:

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! 🙂

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 eg for cables but Luos also told me that he likes to use it for his soul coasters .