Curtis L. Olson wrote:

Hi Harald,

Your screen shots look really nice. Are you using some sort of imposter technique? If you have something workable, please feel free to send early versions to Erik or I for inclusion in CVS. I'm sure there are plenty of others who'd love to play with these. We do have an existing 3d cloud demo in FG, but it was written with an entirely separate scene graph/coordinate system and never fully integrated into FlightGear.

Best regards,


The impostor code is not ready, I still need to call the new RenderTexture class. I must also look at the reposition code because atm the clouds are moving with the plane...I will try to send something next week end.

Jon Stockill wrote:

Nice :-)

Are the additional effects just a "whole screen" effect, or are they tied to the cloud objects so that (for example) visibility is reduced below rainclouds.

A lightning is tied to a cloud and could perhaps cast light around (even if I don't know how).
I thought of "whole screen effect" for rain or snow because I am using the technique described in Niniane Wang paper - a double cone around the camera - to draw raindrops or falling snow. And its easy to reduce the whole scene visibility or light when its raining for example. But I was thinking of adding cloud shadows if the clouds themself don't kill the fps too much.

John Wojnaroski wrote:

Are you using the techniques and algorithms devleoped by Mark Harris that are currently in SimGear? You might want to read his dissertation posted on his web site. Mark has since gone on to greener pastures working for Nvidia.

I don't think there are any snapshots on the website.
John W.

No I am not doing like this. I read his papers (and a lot of others about clouds) but I don't totaly like the method.
He tries to do some realist lighting of clouds and I agree they are nice but first I am not sure that this is fast enough and second I am wondering if this is usefull to do accurate lighting. Water and ice clouds don't look the same, clouds cast shadow on other clouds, etc, lot of things that are hard or time consuming.

I am using some sort of metaballs that are randomly placed in box containers. The cloud is built with a set of positionned box that determine his general shape. For the lightning I first use the classical dot product of normal and light - on each vertex for a smooth shading - this will give a bit of volume and should light the side of the cloud facing the sun and darken the opposite side. This computed light is weightned by an anisotropic factor, and finaly an ambient term is added. Its not realistic but its not too bad too ;)

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