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Monday, January 30, 2017

Prettier, Faster Terrains

We will be updating the terrain systems in Voxel Farm soon. Hopefully, it will get a lot prettier and faster. It is not often you get improvements in these two, for the most part, opposite directions. In this case, it seems we got lucky.

It was thanks to a synergy between two existing aspects of the engine that get to play together really well. One is UV-mapped voxels, the other is meta-materials.

Here is how it works: A single meta-materials describes a type of terrain. For instance, mountain cliff. Within this single meta-material you may find different materials. In the case of a cliff that could be exposed rock, mossy rock, grass, dislodged stones, dirt, etc. An artist gets to create how the meta-material surface is broken down into these sub-materials. The meta-material also has a volumetric definition, which is a displacement map and can be carefully tied to the sub-material map.

When you are close to the meta-material's surface, it must be rendered as full geometry. This is because features in the meta-material, let's say a rock that sticks out, can measure up to dozens of meters. This content must be made of actual voxels so it can be harvested, destroyed, etc. It is not just a GPU displacement trick.

As you are farther away from these features, using geometry to capture detail becomes expensive. You face the hard choice of keeping a high geometry density or dial down geometry and loose detail.

The new terrain system can dial down geometry, but keep the appearance of detail by using automatically generated textures for the metamaterial. For the close range, it still uses geometry to capture detail, but at a certain distance the meta-material displacement can be represented with just a normal map. High resolution sub material textures for grass, rock, etc. are not needed anymore. A single color map is able to capture the look of the metamaterial from this distance. These are only a few extra maps that can be reused anywhere in the scene where the meta-material appears.

The following image shows a single meta-material that uses geometry for the close range and texture maps for the medium-far ranges:

The colors in the wireframe view show where each method is applied. Just by comparing the triangle densities you can see this saves a massive amount of geometry:

This method is not new in terrain rendering, however, it is quite new in a voxel terrain. It is all possible thanks to the fact our voxels can have UV coordinates. Voxels output by the terrain component in the green area have UV coordinates. These coordinates make sure the normal, diffuse and other maps created to render the meta-material at this distance match the volumetric profile and sub-material patterns in the meta-material up close.

The beauty of it is that this work with any type of terrain topology, not just heightmaps. If you are doing caves, cave walls, ceilings and ground are very distinct meta-materials and they would all benefit from this method. And it should be all automatic, we can turn this system on, and it won't require artists to create any new assets.

We are still figuring out how to solve some kinks in the system, but so far I am very pleased with the results. I will be posting more pictures and videos eventually.

Monday, January 23, 2017

Boxes to Voxels to Boxes

MagicaVoxel is an incredibly fun and popular voxel editor. It allows you to recreate that pristine volumetric 8bit look that never was, but we all remember so fondly. We are often questioned whether we could support that kind of look in Voxel Farm scenes, so the team quickly wrote an importer for MagicaVoxel models:

The following video shows the experience, from importing MagicaVoxel models to running a full environment inside Unreal Engine 4:

As you can see from the video, once we began importing these models into the scenes, we figured out it would be nice if the entire world was blocky too. This was now outside MagicaVoxel's realm, but it turned out quite simple to switch off the smooth surfaces in Voxel Farm and make it all look blocky.

A very interesting turn was how to handle the LOD. As I was posting work-in-progress images of this on Twitter I got some interesting feedback. Jens Blomquist, who wrote Blockscape, mentioned he chose not to use LODs in his block game since the larger blocks in the distance produced confusing distance cues. What he meant can be clearly seen in the following image:

Here the boxes in area A should be smaller than boxes in area B.

Paniq (Leonard Ritter) suggested an interesting experiment: What if we used smooth surfaces for distant LODs but keep blocks for near range? It did not turn out well, but it was worth a try:

I found another illusion-based trick that did introduce some improvements: Decrease LOD near player (+2), increase LOD (-2) for buildings, leave far away LOD unchanged (+0). Thanks to the adaptive scene density, the architecture did not need to be degraded so it could remain at the best LOD possible as well:

Then I realized all these were solutions to a problem we should not have in the first place. We were equating voxels to boxes and that was wrong. Instead, we should be using the variable-sized voxels to encode constant-sized boxes. Unfortunately, I did not get to test that theory because lunch was served. When I was done it was time to go back to non-boxy things. Maybe some day in the near future...

Tuesday, January 17, 2017

When Mountains Move

There is an aspect of procedural generation I do not see discussed often. What happens when you have layers of procedural content, add hand-made content on top of it, and then go on to improve the procedural generation?

Last week we did a release of our tools that make it really simple to create terrain biomes. You can see it in action here:

This system can produce fairly good looking terrain with just a few clicks, however, there are still some aspects of it I wanted to improve.

One key issue that you can see in this video, is that it tends to produce straight lines. There is still some "diamond" symmetry we need to address the core algorithm. The image below shows a really bad case, where the produced heightmap has parallel features forming an almost perfect square:

At the left, you can see the generated heightmap. The right panel shows a render of the same heightmap.

This did not take long to fix. Instead of running the generation algorithm on a grid made of squares, switching to irregular quadrilaterals is enough to break most of the parallel lines. The following image shows the results after the fix:

A simple fix or improvement like this leaves us with bigger questions: How do we make this backward compatible? Do we make it backward compatible at all, or just apologize and ask human creators to relocate their data?

We could provide an option to turn this improvement off. That would be the most diplomatic approach. But then what about any other improvements we have planned for the future, do they all get their own setting? At this point, it seems we would be complicating the UI with many options that are meaningless to new users. These would be just switches to make algorithms behave in more primitive forms.

Whenever algorithms create content along with humans it really becomes a muddy, gray area for me. I still haven't figured this one out.