Flow noise addendum: localizing advection

The advection vector doesn't have to be a constant: with some tweaking we can localize must of the vorticity to a single point on the sphre

Determining the distance to a point

The flow noise presented in a previous article has an advection parameter that determines how much small details are swept along with turbulent larger features. There is however nothing that prevents us to make this parameter dependent on the distance to some location to introduce some variation in the overall swirl patterns on the the sphere. An example is shown in the next video sample where the vorticity has its maximum near a point on the lower right front side:

Example node setup

The node setup looks like this:

The nodes in the yellow box calculate the distance to some hotspot ([1, -0.3, 1] not visible in this screenshot) and then calculate the lenght of this vector by determining the inproduct with itself. Then we add one to prevent division by zero in the next step, where we calculate the inverse. By raising it to some power we can control the 'tightness' of the spot, i.e. how fast our value decreases when we are further away from the hotspot. The final multiply node gives us some control on how strong the overall effect is.