Thread by @craigperko

Well, I was stuck on the Sam & Max remaster's only bad point last night. The ambient occlusion was so awful I woke up at 4 AM thinking about it.

So let's talk about big cartoon mouths.

Small human mouths don't really move much. You can presume the back teeth are hidden and the front teeth can be simply lit because that's how tiny human lips work.

The problem is that as the mouth gets bigger, you see a lot more of the teeth.

You see the outsides of the teeth as their cheeks roll back, you see the crowns and the inner faces as they open their huge, hinging jaws.

Cartoons are really disturbing if you think about it.

Anyway, how are the teeth lit when this sort of nonsense happens?

For the most part, the answer is "naively". You can see this in a lot of games where someone opens their mouth and the inside of their mouth glows like the sun.

It's receiving no shading information from the head, let alone bounce/indirect information from the lips.

That's fine when you only ever see the front teeth. But it gets strange when you can see the rest.

It'd be extremely expensive to calculate per-frame lighting information about teeth, so most games that need to do something about the back teeth use some kind of occlusion calc.

Here's an example of how that looks. Not too bad, right?

Not too bad... in a still frame. The problem is that it's using screen space data to do it.

So... that means it warps and jumps and morphs every frame based on the camera angle.

(This game also uses some basic shadow calculations, but clearly they decided that wasn't enough)

Screen space ambient occlusion is used in nearly every modern game, because it works very well for scenery.

However, it doesn't work well in situations where organic edges constantly roil past each other, because we see the calculation exposed with each frame.

So I was thinking... why not just use a simple texture driver?

We do it all the time. For example, we might use a driver to reshape the shoulder so it looks right during arm-raise animations. Or a driver to move combinations of shape keys that make Sam smile.

Why not have a driver that simply darkens or brightens the teeth according to how open the mouth is, how furled the lips are?

You could just use a gradient and move the zero point.

It wouldn't be realistic, exactly.

But at least it wouldn't FLASH.

Anyway, if you're listening, Skunkape: your ambient occlusion is really distracting but everything else is great.