How to layer the Worley noise like this?

Question

Recently I'm trying to implement Siggraph15_Schneider_Real-Time_Volumetric_Cloudscapes_of_Horizon_Zero_Dawn, you can also find this in GPU Pro 7, (part II Lighting, chapter 4, Real-Time Volumetric Cloudscape).

I can make the first Worley noise above and increase the frequency, I can get another Worley noise, but how to blend the two noise to get the middle noise and finally, the third noise"?

The last image is two single frequence worley noise and the result I blend them.You can try your method with them.

My formula is this:

tmp = (worley1 + smoothstep(0, 1, worley1)*worley2*0.5) / (1 + smoothstep(0, 1, worley1)*0.5);
tmp = ReMap(0, 1, 0, 0.7, tmp);

ReMap is:

double ReMap(double oldMin, double oldMax, double newMin, double newMax, double src);

Note that worley1 and worley2 is worley noise range from 0 to 1.The result is close in the first glance,but it's not the same apparently. I think the formula is TOO tricky and maybe I got something wrong.

Answer 1

Using an image editor, I was able to get close as follows:

• layer the image on the right over the top of the image on the left
• reduce the opacity of the top layer to ~66%
• merge layers
• auto level resulting image

I think the equivalent operation would be something like normalize((A + (0.66*B)). The contrast was a bit too sharp, so I suspect a full normalization is not quite right. Maybe mellow it back out with something more like:

C = A + (0.66*B)
D = (normalize(C) + C) / 2

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If you want to combine two layers such that "the black part in the first image still be black in the result texture", try this instead:

C[x] = Min(A[x], B[x])

Note: this assumes that black = 0.0 & white = 1.0.

Answer 2

float blend1 = 0.3f;
float blend2 = 0.3f;
//blend worley1 and worley2
float t = worley1 * (1.0f - blend1) + worley1 * worley2 * 1.25f * blend1;
//blend t and worley3
float t2 = t * (1.0f - blend2) + t * worley3 * 1.25f * blend2;
//revert perlin and scale it, enlarge the perlin noise according to the worley noise
float reuslt = ((1.0f - perlin) * 0.65f) / (1.0f - t2 * 0.6f);

Answer 3

I'm so excited that I found a blog about how to get the awesome cloud.

I download the source code (link below) and read it.

It blends the Worley noise like this:

tmp = worley1 - (1-worley2)*0.25;
tmp = saturate(tmp);

Frankly speaking,the result is analogous with mine. But the method is quite simple and NOT that tricky. And I prefer this one.

The link is:http://bitsquid.blogspot.com/2016/07/volumetric-clouds.html

The result is like this. It's no doubt that this is the right solution.

Thanks for Jon and Pikalek anyway^_^.