Fire is a common element VFX artists need to work with in television, film, commercial, and web content. In a previous lesson, we looked at where to find fire elements and how to quickly composite them into your scene. In this lesson we are going to take the fire composite one step further and add heat waves into our scene. Adding heat waves is more of a judgement call made by the compositor if he feels the element is necessary. But in the case of a larger, hotter fire, the area above and surrounding the flame becomes slightly distorted from heat rippling in gas form.
To create this heat rippling effect, we first want to create a new solid in our composition (I named mine DISPLACEMENT) and then go to EFFECT > SIMULATION > PARTICLE PLAYGROUND.
That red funnel is called the CANON. Move the canon to the core of your heat source (in my comp I am using the fire element as my source).
First thing you will want to do is increase the BARREL RADIUS so that the particles stretch horizontally with the width of the heat source. Increasing the barrel radius will stretch the particles in both X & Y directions. Using the POSITION controls, adjust the particles to begin at the base of the of the heat source (not below it).
Now we need the particles to increase and match the speed of the heat source (in my case the fire). To do that, increase the velocity in the particle playground settings (aka speed) of the particles. For me, somewhere around 150 did the trick. The particle speed now looks good, but towards the end of the particle’s life it begins to slow and dip back down. I want the particle to continue a smooth trend upward. To fix this, I can reduce the particles GRAVITY FORCE to 0. With the gravity set to 0, there is no source to pull the particle back down to earth.
The last thing you will want to do with the particle playground itself would be to increase the PARTICLE RADIUS to around seven or so. The size of the particle will determine the size of the wave. Keep this in mind as you decide how subtle or obvious you want this heat wave to appear.
With our particle system running the way we want it, let’s duplicate it! We will want to change the duplicate particle from RED to GREEN and adjust the velocity setting slightly so that it doesn’t follow the exact same path as the first particle system.
We now need to pre-compose these two particle systems together by highlighting both in the timeline and hitting COMMAND+SHIFT+C on the keyboard. Be sure to move all attributes and name this as WAVES COMP.
To finish, select the WAVES COMP and go to EFFECTS > DISTORT > DISPLACEMENT MAP. Under the effect controls, go to DISPLACEMENT MAP LAYER and change it to WAVES COMP. This will use the WAVES COMP as its reading source for the displacement; thus creating the heat waves. To control the amount of displacement, you can increase and decrease the vertical and horizontal displacement controls to your liking. There you go! Heat Waves!