Create water surface using particles

in the last video we saw this preview of a shot from Finding Nemo where we've drawn the particles as balls to illustrate their motion for the final shot we use the particle positions to compute a surface then we render that surface to look more like water to draw a smooth surface using individual particles we use an analogy involving heat first imagine these particles are little heaters next pretend we have a thermometer which tells us the temperature at any point in space for example the particles might be exactly a thousand degrees and as we move away things cool down let's say this point over here is exactly a hundred degrees and there isn't just one point in space which is a hundred degrees but many points so if we connect all points where the thermometer says 100 degrees we get a curve shown here in yellow and that's the trick now we can fill in this yellow curve with a solid blue color to give us something that looks more like a puddle of water if the particles are far apart they each form their own isolated region like a droplet as they get closer the droplets start to glob together then making real water here's a version with a few more particles this is starting to look like water it would really look like water if we had a few thousand particles for use in our movies we work in three dimensions and the curve becomes a surface like in this shot from finding dory or in this more extreme water simulation also from finding dory here's an example from monsters University here we're simulating paint instead of water we've turned up the viscosity since paint is more viscous than water we weren't exactly sure how paint would behave so one of the first things we did to create this shot is to videotape reference of real paint the reference really helped us create a believable look let's pause here so you can practice using the next exercise good luck