Oil pixels float on top of water pixels, sand pixels sink. Fire pixels burn better on oil pixels, and will evaporate water pixels. No – I haven’t gone mad, I’m describing Yarik’s Element Dots canvas demo where different coloured pixels represent different elements and you can set up different scenarios to see how they get along.
When you first load Element Dots you are presented with three taps, representing pouring water, sand and oil. Draw on the canvas with the solid brush (which appears to represent grass) to contain your elements. Then select an element from the right hand menu to add to the mix.