I created a looping fire with a vector flow map for my game, but I noticed that the edges and tips of the fire appeared “steppy,” particularly near the top where the flames fade. This issue is most noticeable in the less intense, faded areas, while the hotter, denser parts of the fire appear correct.
I was able to trace the issue back to the vector map.
Here’s a comparison of one of the frame’s in the flame:
As you can see the less intense areas of the flame on the albedo, on the vector map are very faded and thus moving the flame a less and incorrect amount.
To confirm the issue, I created two new flames with no turbulence for clarity. I also reduced both the inner and outer blur on the vector map to help highlight the problem.
Weak flame with less fuel:
Strong flame with more fuel:
As shown, the vector map for the weak flame is faded, resulting in incorrect and inconsistent motion vector data compared to the rest of the fire.