As a final flourish, I add a simple particle system to simulate ash. And with that, the effect is done—until it’s not. Iteration continues, and the needs of tomorrow may outweigh the needs of today.

But that is another problem! One at a time.

In the way these things sometimes happen, this works perfectly the first try.

Until it works! In the end I add a vertical blur to let the distortion “rise” off the lava. I also tweak the noise for less intensity, and add a cosine wave to the original sine wave, using a different amplitude and frequency. I’m happy with the distortion pattern now, but something’s still missing.

So much of this kind of work is iteration. You have an idea, you test the idea, you modify the idea, you test again. This thing I thought would work is too subtle, what if I multiply it? My code is broken, what error did I get? One problem at a time, over and over, and over again

We’ll try a blur so that the mask softens and expands. This looks much nicer in this view, but will certainly need adjustment for the final effect. I can already guess that it'll need the gamma boosted, or a directional blur of some kind

Let’s switch views to see the mask channel itself. We can see our perlin noise texture, and how it has the harsh edge of the lava tiles.

Returning to our heat filter—and—it works! Well, it masks to the right layer. We still have to figure out this distortion effect. And the next thing I want to try is expanding the mask—looking at it now, it's become too subtle, only visible around the lava edges, in a way that’s easy to miss.

That did not do the thing! At first glance I thought it did nothing at all, probably I screwed something up and broke the shader. But looking closer, it *is* distorting, and it is masking—just not on the right layer. So something is up with how we’re reading or writing the depth value, maybe

This *should* enable us to mask on the lava layer by simply checking that `originalDepth == lavaLayerDepth`. And because of the way the depth buffer overwrites ‘further’ values with ‘nearer’, we get occlusion for free. In theory! So let’s spin that up… and… hm.

Take two: I decided to try masking the distortion with a scrolling perlin noise texture. This definitely cuts down on the intensity, but I’m still feeling queasy looking at it. At this point I’m now certain that the final effect cannot cover the whole screen.

My first attempt: a simple sine wave applied to the whole screen. Partly this was to be sure I’d set up the shader correctly, partly this was to see if sine distortion could work as a starting point. Verdict: uhhhhh I’ll get back to you, I immediately have a headache

This has turned out all right! So I thought I’d do a little thread on it. For reference, this is what I started with—a typical fire-y area with no vfx applied. I quite like the lava animation my brother made, but I’m aiming to add just a little extra “this place is hot, like so hot you guys”