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Hunting Clouds!




One of the most well-known X-Plane 11 issues is its cumulus clouds rendition.

The default clouds engine seems to handle stratus clouds much better because of the structures it tends to create, as well as the clouds textures it uses to work.
My main aim was (is) to get a believable rendering of cumulus clouds without changing the default engine too much.
It was difficult, but I think I found a pretty decent way to combine textures to make some realistic looking formations.
I divided every cloud formation into three parts:

  1. cloud base: it needs to be darker than the top and usually softer. Some refracted light could filter through the cloud, and the texture must show such refracted light.
  2. cloud body. It's usually lighter than the basis, convective currents prevail and the cloud develops vertically to form cumuliform structures
  3. cloud top. It's the highest part of the cloud formation, here convective flows stop and reverse, thus causing the birth of the characteristic "cauliflower" shaped tops.Clouds tops need to be light and sharp, and they must feature a neutral illumination to avoid shading artifacts when the sun moves around the sky.




The cloud species shown in the pictures are "cumulus mediocris" and "cumulus congestus", cloud formations that can be usually found in approacing cold fronts, or fair convective weather.




I took all the photographic data, here some of the samples I used.







Alert! These are only ideas for now!


My intention is to create a simple script which influences the default XPlane cloud textures organization: it will divide the sky into three regions influenced by the angle sunlight hits the clouds.

  1. Front Light region: sunlight directly hits the clouds, so every cloud in such region is fully lightened.
  2. Side Light region: sunlight laterally hits the clouds, so every cloud in such region is half lightened, half shadowed. This region is divided into a left region and a right region where textures are projected in a specular way (other samples could also be used to improve the overall variety)
  3. Back Light region: clouds shadow the sun, light refraction effects are visible.





These three regions will only influence the rendering of cloud textures from cloud_puff_3 to cloud_puff_5 (far away clouds, and not proximal puffs), which are "pure 2d clouds" in default XPlane cloud rendering engine.

So there will be three "cloud_puff_3" , three "cloud_puff4" and three "cloud_puff5" textures for each cloud textures set (2 or 3 maybe)
Clouds puffs from 0 to 2 won't be influenced by this partition and will follow the normal X-Plane organization to give a 3d illusion.


Such cloud texture partition should improve a lot the overall sense of realism, and will also provide a correct illumination model for the farthest clouds.
So this is the first basis I put to build the future TrueHaze system.
Now I need some more ideas to improve stratus clouds and cirrus clouds rendition.

As I said, the (not so little) problem is I'm not able to build such script actually.



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