Video Update for April 2013

An update about clouds and a surprise topic for the second part.


Making these recordings feels a bit weird. I love talking to real audiences, but this feels more like leaving a message in someone's answering machine.

The Unity plugin is looking good!

Here is an update on the Unity front. Let's see if a screenshot is worth a thousand words:

This is the same terrain generation you see in other screenshots and videos I have posted. This image in particular was not created by me, but by some very talented guys who took the Voxel Farm engine and are using it from Unity.

The sky and clouds in the screenshot is a box with a static image on it, it is not related to the clouds and sky streak of posts I had earlier. The thing is, once you are in Unity there are several plugins that will do real-time skies for you. Actually there are plugins that will do real-time anything for you. That is the point. We are hoping to become another one.

Some Clouds

Clouds come in many forms. When it comes to generating them it seems there is no silver bullet method. Part of the problem is we call clouds to just one aspect of a more general process: water particles suspended in air. This could also be fog, or the misty breath coming out of trees and plants in a jungle. This is what the initiated in this occult science call "The Participating Media".

I decided to tackle this problem by having different layers working together. Which layer to do first? Even in the highest places in Earth, it is likely to find a layer of clouds over your head. I did some experiments over the weekend on how this particular layer could be rendered.

Here are a couple of early screenshots for your consideration:

It is a very simple and fast method that allows clouds to animate and evolve over time. You can go from a clear sky to a very cloudy one as well. It takes into account the sun's position and does some basic scattering and self shadowing.

These clouds are rendered in the same skydome that performs the day-night cycle, so they do not add any new geometry. This is also the problem with this method: This is a flat layer. There is the impression of volume thanks to how the light is computed, and this trick holds as long as the clouds do not move too fast. If you make them sprint over your head it becomes obvious it is a flat layer. You cannot also come too close to these clouds, that also kills the illusion.

For what it does, I think the method is quite neat, especially if you don't have much GPU cycles to spend in clouds. It does not use any textures or any other resources. This is 100% GPU so it would run nicely in demos or WebGL frames. I think it deserves a future technical post on its own, that of course assuming you guys like how they look.

Let me know what you think by dropping a comment.

The sun rises in ProcWorld, again

Last week I posted some early screenshots of the nigh-day cycle. There was a lot going wrong in them and you guys were very helpful in pointing out solutions.

I did another iteration on this, while not everything is as it should, I think there was some improvement. This time I have captured a video. The transitions are better appreciated like this. Again let me know what you think.

The main issues with the previous iteration were the brightness of the sky (or lack of it), and how the distant features failed to blend with the sky. This time I made sure there was enough atmosphere so more light was trapped between the horizon and the eye. The distance to the sky is also consistent with the terrain dimensions, now the colors in terrain and sky match better.

A few comments in the previous post suggested a different method called "Precomputed Atmospheric Scattering". It certainly produces better results than the method I am using here, which is the one from O'Neil in GPU Gems 2.

I had a quick look at the method and saw that in its vanilla form it could run slower than what I have now. While the method uses precomputed tables as textures to accelerate rendering, all the work is done in the fragment shader. That means every pixel on screen now had to perform two or three additional texture fetches.

The method from O'Neil does all the heavy lifting in the vertex shader. Consider this scene:

The sky, even if it appears softly shaded, has only a few vertices:

I think in this case it makes a big difference.

The precomputed method could also run in the vertex shader, but then it would take some time to port the tables, which now are in pixel formats that cannot be read by the vertex shader.

Of course there is a chance I am reading this wrong. If you have worked in this area before and see what I am missing please let me know.

The sun rises in ProcWorld

So I finally added some proper light scattering to the sky atmosphere in the realtime demo.

I am using the classic approach devised by O'Neil, which produces great results but it is also very sensitive to any change in the input parameters. A lot of tweaking is still required.

Here is a series of shots, keep in mind this is a work in progress but any early comments surely will help.