CloudWright 1.8

CloudWright 1.8 is now available for download. There are lots of improvements, including a neat feature that lets you script your own exports.

Notes on the sky

The best way to get a good-looking sky in your game or simulation is to use Simul Weather. But those who have an interest in such things, and time to spare might like to try writing their own sky scattering model. The first place to go in this case is usually to the 1999 paper on scattering by Preetham et al., where the basics of Mie and Rayleigh scattering are outlined.

Scattering is the process that turns the sky blue – light passing through air is scattered away from its direction of travel. Blue light is scattered more than green and red, so the sky is blue, and distant objects acquire a blue cast. But any light that was travelling towards the viewer to begin with is also scattered – again, more blue than red and green – so distant clouds can appear yellow, and the sun at dawn appears red.

Implement the Preetham model and you’ll get the basics of a blue sky with a bright horizon. You’ll need to include both Mie and Rayleigh scattering to get the right effect, and some of the more obscure terms are necessary to get the right look for twilight – plain Rayleigh scattering turns the whole sky yellow at sunset, which is quite a common look in games, but practically unheard of in reality. You may also find that the horizon is too bright, and the zenith too dark, even in daylight.

The yellow twilight effect is actually not a failing of the model, so much as the “blue twilight effect” is an additional quality of the sky that can’t be modelled with single Rayleigh or Mie scattering alone. You need to bring in some of the more advanced properties of the atmosphere to get the correct, blue sky at twilight. The over-bright horizon, and dark zenith are much simpler to correct. It’s not your model that’s at fault, it’s your monitor.

Simul Weather licensing information

Rather than informing people on an individual basis, I decided to put the costs for licensing Weather up on a page of this site. There’s also a neat little form for licensing enquiries, so there’s really no reason not to get in touch!

Evaluating Simul Weather is really very straightforward – you put the libraries in the right place, cut-and-paste the sample code and you’re away. We’re confident this is some of the easiest middleware to use, and we’re always looking for feedback.

CloudWright for XSI – try it now!

We’ve got CloudWright for XSI in open alpha – this means it’s a very early version, but the main features are in, including live sky previews in DirectX. You can download it from here.

Gamma correction

The sky is usually the brightest part of a given scene, and often saturates – if the rest of the scene is normal brightness, parts of the sky will be too bright for the display to cope with – they appear white.

This can be made worse if you don’t gamma-correct your image. Monitors – CRT’s and LCD’s are non-linear displays: they perform a gamma-operation on the image you send them, so you don’t get the colour you ask for.

CloudWright 1.6.1

So we’re taking CloudWright 1.6 out of Beta, and into version 1.6.1 now. It’s a great version, lots of little issues fixed and a couple of great new features, more about which soon.

XSI CloudWright Update

As previously announced on some of the forums, we’re making CloudWright for XSI just now. The release schedule is up in the air but we’ll be getting an alpha/beta version to existing customers within the next few weeks. It was going to be before the holidays, but the plan now is for sometime in January or February. Initially it will have much the same feature-set as the standalone CloudWright, but we’ll later introduce some more precise control for cloud-shape etc. Mainly, the plug-in will be very tightly integrated with the way XSI does things. Luckily, this fits quite well with the way CloudWright works, and this is why we’re starting with XSI. Later we’ll have plug-ins for the other main 3D packages.

If you’re an XSI user and interested in what we’re doing, get in touch!