http://http.developer.nvidia.com/GPUGems3/gpugems3_ch13.html

Would it be possible to get the above effect while using alphas from a model+texture? I ask because our cloud system works like so:

We create a cylinder object that rotates in a selected direction ( slowly ).

To get the desired cloud effect we apply a texture to it using SRGB and Alpha layer to remove the areas we do not want to cover by clouds.

Our desire is to use the dome ( which encases the cylinder and the world ) where we apply the sun and generate the GPU gems lighting ( god rays ) from the clouds that are showing. I guess the question is, is there any way to create the same desired effect by using the Cloud system we have in place?

I tried that in your almost exact same situation, but it was a failure (only 2 days spent on it though).

For two reasons:

- difficult to find the correct smearing direction for each pixel, though I'm sure there is a way had I put a bit of effort

- serious issue with desaturation over the whole sky. to have "god rays" somehow you need to "add haze" and that is terrible for the result. your image becomes whiter and desaturated overall. I tried various operators; like multiplication, or mix of mul and add, none were good. anyway, consider using somekind of pow() function to add godrays only near the solid angle that subtends the sun. Because physically, in-scattering mainly happens on light paths around this angle anyway.

- impossible to use with tiled rendering.

I will add one reason that could be a bother to your particular case, you have animated clouds so you will need to re-run this. but it is damn costly (100 samplings per pixel) so I suggest you use the fact that your rotation is very slow to smear progressively (in multiple passes over multiple frames).

But again, if I were you, I would still attempt this method, it seemed the easiest and best fit for cool results in a simple fasion for this case. I'm just saying it will require serious engineering. Kenny Mitchell gives us a theory, in practice it's always another story.

Well, the inital test proved.... some what interesting. We used only the GPU gem tutorial and we got it working....

But the cost of this was damn near 250 fps ( normally i get 350 or higher ). This would be a serious blowback for any rig since my machine is pretty beefy. That said, we have not optimized nor do we know if it is all correct. We do have some ideas on how we could get away with such things but the biggest part is that we got it working. I will keep you guys posted as we travel down this road. Any further suggestions or hints let us know! Thanks btw

Shader code is the exact same as that I linked in the first post. We mimicked the GPU gems. Not sure what you mean by FPS is not a measurement of cost. If i have 50 shaders and my FPS goes to 10 because of those shaders It is very much cost related. This is not a flight sim where 5 or 10 FPS will do so it is very much a relation to cost. You may have some valid point related to code as to how FPS = MS but in the world of the common person ( me ) FPS is the measurement of cost because it defines whether something is worth the effort or not to implement.

Shader code is the exact same as that I linked in the first post. We mimicked the GPU gems. Not sure what you mean by FPS is not a measurement of cost. If i have 50 shaders and my FPS goes to 10 because of those shaders It is very much cost related. This is not a flight sim where 5 or 10 FPS will do so it is very much a relation to cost. You may have some valid point related to code as to how FPS = MS but in the world of the common person ( me ) FPS is the measurement of cost because it defines whether something is worth the effort or not to implement.

Thank you for this help, I will have Goss try to add that in later today when he gets up.

As for the FPS, thank you for explaining it as I now have a better understanding of what you mean.

I saw that tutorial.... hm.. okay thanks. This is great information and I appreciate it.

Not sure where goss took these links but this is what we have so far:

This is with 0 optimization and more or less just a test to see if it works correctly.