Ocean Rendering

Let me first say that I'm often visiting my own blog to read how I did certain things. This is mostly true for some of the older, more technical posts. I decided to blog about recent water rendering development in a way that will be helpful for me in time when my brain niftily sends all the crucial bits to desert. I apologize in advance if some pieces seem incoherent.

Now for the rendering of water in Outerra.

There are two types of waves mixed - open sea waves with the direction of wind (fixed for now), and shore waves (the surf) that orient themselves perpendicularly to the shore, appearing as the result of oscillating water volume that gets compressed with rising underwater terrain.

Open sea waves are simulated in a usual way by summing a bunch of trochoidal (Gerstner) waves with various frequencies over a 2D texture that is then tiled over the sea surface. Obviously, the texture should be seamlessly tileable, and that puts some constraints on possible frequencies of the waves. Basically, the wave should peak on each point of the grid. This can be satisfied by guaranteeing that the wave has an integral number of peaks in both u,v texture directions. Resulting wave frequency is then

Other wave parameters depend on the frequency (or its reciprocal, the wavelength). Generally, wave amplitude should be kept below 1/20th of wave length, as larger ones would break.
Wave speed for deep waves can be computed using the wavelength λ as:

Direction of waves can be determined by manipulating the amplitudes of generated wave, for example the directions that lie closer to the direction of wind can have larger amplitudes than the ones flowing in opposite direction. The opposite wave directions can be even suppressed completely, which may be usable e.g. for rivers.


Shore waves form as the terrain rises and water slows down, while the wave amplitude rises. These waves tend to be perpendicular to shore lines.

In order to make the beach waves we need to know the distance from particular point in water to shore. Additionally, a direction vector is needed to animate the foam.

Distance from shore is used as an argument to wave shape function, stored in a texture. This shape is again trochoidal, but to simulate a breaking wave the equation has been extended to a skewed trochodial wave by adding another parameter determining the skew. Here's how it affects the wave shape:

The equation for skewed trochoidal wave is:

Skew γ=1 gives a normal Gerstner wave.
Several differently skewed waves are precomputed in a small helper texture, and the algorithm chooses the right one depending on water depth.

Distance map is computed for terrain tiles that contain a shore, i.e. those with maximum elevation above sea level and minimum elevation below it. Shader finds the nearest point of opposite type (above or below sea level) and outputs the distance. Resulting distance map is filtered to smooth it out.
Gradient vectors are computed by applying Sobel filter on the distance map.

Gradient field created from Gaussian filtered distance map

Both wave types are then added together. The beach waves are conditioned using another texture with mask changing in time so that they aren't continual all around the shore.

Water color is determined by several indirect parameters, most importantly by the absorption of color components under the water. For most of the screen shots shown here it was set to values of 7/30/70m for RGB colors, respectively. These values specify the distances at which the respective light components get reduced to approximately one third of their original value.

Red: 7m, Green: 30m, Blue: 70m, Scattering coefficient: 0.005

Red: 70m, Green: 30m, Blue: 7m

Another parameter is a reflectivity coefficient that tells how much light is scattered towards the viewer. Interestingly, scattering effect in pure water is negligible in comparison with the effect of light absorption. Main contributor to the observed scattering effect is dissolved organic matter, followed by inorganic compounds. This also gives seas slightly different colors.

Scattering coefficient: 0.000

Scattering coefficient: 0.020

Here's a short video showing it all in motion.

An earlier video that was posted on the forums with underwater scenes:

TODO
Water rendering is not yet finished, this should be considered a first version. Here's a list of things that will be enhanced:

• Better effect for wave breaking. This will probably require additional geometry, maybe a tesselation shader could be used for that.
• Animated foam
• Enhanced wave spectrum - currently the spectrum is flat, which doesn't correspond to reality. Wave frequencies could be even generated adaptively, reflecting the detail needed for the viewer.
• Fixing various errors - underwater lighting, waves against the horizon, lighting of objects on and under the water, LOD level switching ...
• Support for other types of wave breaking
• Integrating climate type support to the engine, that will allow different sea parameters across the world
• UI for setting water parameters
• Reflect the waves in physics for boats
  

A few of ocean sunset and underwater screenshots that were posted on the forums during the development.

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Outerra Year 2010 Retrospective

Our friend from Texas, artist and science-fiction writer born under nickname of C. Shawn Smith, made this nice compilation from pieces of our published and some unpublished videos created during the year 2010.

Outerra 2010 Retrospective

Thanks Shawn, and happy New Year to all our fans and supporters all around the world!

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Aeroworks and Outerra

This blog post will be about our recent visit of AeroWorks team at Brno University of Technology in Brno, Czech Republic. These guys are working on SimStar project, a light aircraft simulator based on the cockpit section of Evektor SportStar aircraft.

Presentation photo, the space is actually jammed with stuff as anyone would expect

They were interested to use Outerra as one of the image generators that could be plugged in. We liked that idea as well, so ultimately we packed our stuff and went on a trip to Brno, which is just some 125km from our HQ in Bratislava.

The project is being led by Peter Chudy who is coaching a few enthusiastic students working on related diploma theses with goal of enhancing the simulator. He is also ensuring that everything in this unique academic project goes right, undertaking all the necessary chores and dealing with all companies that might help to advance it. Peter is quite dedicated kind of guy who constantly fires jokes intermixed with questions caring whether we like the project. Nevertheless, or maybe thanks to that, he was nicknamed "Mr.Horrible", not just for forcing people to take off their shoes

Mr.Horrible ready to take off in Outerra

Approaching Airport2. Displays are not yet interconnected with Outerra, but otherwise they function just fine.

There were some issues with joystick detection and behavior, and we had to fix the blocking ones directly in place to be able to test the simulator. We still have to adjust the profiles for individual axes to get a more realistic behavior.

The canvas has resolution of 1024x768 pixels which is quite low, the overall feeling will be even better when the projector is upgraded.

Here's also a video montage of initial testing with Outerra as a visualizer. Because of the joystick issues the aircraft control was very clunky. But as a first test it was overall success, all the issues will be dealt with in coming time.

For further steps we'll need to design a protocol for interconnecting all the components of the simulation, or to find a standard one that will suit our respective needs. One of the possibilities is CIGI from Boeing, but its design is somewhat old and doesn't entirely fit our architecture. If anyone knows about other possible standards that we might consider for the job, please let us know.

Forum topic for discussion.

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