Curl-Noise FlowInk stirred by an invisible current that behaves like a real liquid: it swirls and folds endlessly but never piles up or leaves empty gaps, because the flow can’t be squashed or stretched — only sheared.Real fluid simulation is slow: you must keep solving for pressure to stop the fluid compressing. In 2007 Bridson, Hourihan and Nordenstam noticed a shortcut — take any random hill-and-valley field and follow its contour lines instead of its slope, and the flow you get is automatically incompressible, no pressure solve at all. It became the standard trick for smoke and dust in film.