Basic environment sounds

We have added sound system (based on OpenAL), and provided aircraft with engine sounds using preliminary sound samples. Once the sound system was working, I went to add some basic environmental sounds so that the world feels more alive.

The whole system works by sampling coarse level environment data points surrounding the camera, using a 5x5 cornerless grid. Sound emitters are then set up at the places of the points, and each emitter is assigned a sound buffer corresponding to the type of environment.

To hide the grid layout, the emitters are set up to start attenuating the sound only from a distance that is larger than half the grid step. This works almost alright, except that the unattenuated zone also spans upwards, which doesn't feel natural. Later we'll have to implement a custom attenuation function that will handle it.

At the moment there are just 4 environment types - grass, open sea, shoreline and forest. Each emitter of given type can use only one of two sound samples (for now), that are pseudorandomly picked for given location. Locations are identified using a global unique identifier; this identifier is also used to manage the reuse of sound emitters.

Apart from these ground sources there is also another layer of emitters that are used to provide sounds of wind and rustling of tree leaves. They are positioned higher above the ground.

Following video shows it in action. The sound of wind in the last part of the video (in forest) is too loud, especially when the leaves and branches aren't moving yet.

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In other news, we have started a closed beta testing of our alpha demo (yea, beta of alpha ). Here's the announcement and some info from it.

It goes pretty well, meaning we are getting lots of crash and bug reports and unexpected behavior reports on various combinations of hardware, OS versions and internet settings.
It's keeping us quite busy at the moment.

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There's also a new truck model with digital camouflage texture, that we want to use for our demo game:

The camouflage is a modern type that is apparently not so well-known, and from the initial reactions it seems that Minecraft has spoiled it for people who didn't know about it before :-)

White balance

When implementing the fog mentioned in the previous post, I observed a weird thing happening: the fog wasn't white, as I expected, but it had a dirty Beige tint making it look a bit like a smog or something. But since the implementation didn't use different absorption and scattering coefficients for RGB components, and thus the color of the sun light shouldn't have been modified, I thought it was a bug, and neglected it until most of other issues were solved.
But then, after inspecting all the code paths, I came to the only conclusion that the computation is right and the problem must be in the interpretation. So I tried to convince myself that the fog must be white, and the tint actually isn't there. Almost made it, too.

But the machine coldly asserted that the color wasn't white as well. Didn't bother with any hinting as to why, though.
Apparently the incoming light that was scattering on fog particles was already this color, even though the sun color was not modified in any way, unlike in the previous experiments.

Interpretation?

The thing is that sunlight really gets modified a bit until it arrives to the planet surface. The same thing that is responsible for blue sky causes this: a small part of the blue light (and a smaller part of the green light too) gets scattered away from the sun ray. What comes down here has a slightly shifted spectrum.
But how come we see the fog white in real life?
Turns out, everything is fake.

The way we perceive colors is purely subjective interpretation of a part of the electromagnetic spectrum.
And as it is easier for the brain to orient in the environment when the sensors don't move, it is also simpler to stick with constant properties on objects. Our brain "knows" that a sheet of paper is white, and so it will make it appear white in wildly varying lighting conditions. This becomes apparent when you use a digital camera without adjusting for the white color - the results will be ugly.

So basically that's why we have to implement an automatic white balancing, at least until we all have full surround displays and our brains magically adapt by themselves. By the way, playing in fullscreen in the dark room with uncorrected colors slowly makes it adapt too.

Implementation

Our implementation tries to mimic what the perception actually does. By definition, a white sheet appears to be white under a wide range of lighting conditions. So we are running a quick computation that uses the existing atmospheric code on GPU, that computes what light reflects off a white horizontal surface. The light has two components - sun light that reflects at an angle and its illuminative power diminishes as the sun recedes from zenith, and the second one is the aggregated light from the sky. Once this compound color is known, we could perform the color correction as a post-process, but there's another way - adjusting the color of sun so that the resulting surface color is white. This has an advantage of not affecting the performance at all, since the sun color is already taken into equation.

While this algorithm doesn't mimic the human perception precisely, i.e. the actual process is more complex and depends on other things, it seems to be pretty satisfactory, though I expect further tuning.

Some of the properties: it extends the period of day that seems to have a "normal" lighting, and removes the unnatural greenish tint on the sky:


During the day it compensates for the brownish light color by making the blue things bluer. Can't say the old colors were entirely bad though.

So long, and thanks for all the fish

Fog and dust

In addition to the existing atmospheric model that already accounts for aerosol particles in air, we have been working also on incorporating ground fog and dust. It's defined by several parameters that determine its density, light scattering properties and boundary altitude. Shaders then compute resulting attenuation and scattering of sun light for terrain and objects. The code is similar to the code computing optical properties of water, using different values and omitting the upper reflective layer.

Viewing valleys of fog from a greater distance, illuminated by evening sun.

When the amount of scattering is lowered, one gets appearance of dust. Also, thicker layers of dust/mist can cast the terrain down below into darkness

There are several things that need to be done yet - currently the fog settings act globally, covering the whole planet in a veil of mist. There's no modulation that would give the fog a nicer, non-uniform look.

Ultimately, fog (or dust) should appear dynamically according to a probabilistic model that would describe chances of it forming at a given place (climate, precipitation) on the planet in given time of day/year. Or using a real time weather report feed.