Halloween, (CSS) Masks, and Logic Gates

On this site, there is a weekly Meme Monday thread where I normally publish the comiCSS cartoon and look for inspiration. Last week, @webbureaucrat shared a cartoon that caught my attention:

I found it funny and decided to create my own version with HTML and CSS using masks.

At first glance, the first row seemed easy to make: two radial gradients and picking the best mask-composite. The second row seemed more challenging. Would adding one extra gradient be enough?

Ignoring the lines and jack-o-lantern face features —that would be added later—, the base of the cartoon would be two circles that intersect. To achieve that, I created a mask with two radial gradients:

.pumpkin {
  mask:
    /* trick */
    radial-gradient(circle at 40% 60%, #000 25%, #0000 0),
    /* treat */
    radial-gradient(circle at 60% 60%, #000 25%, #0000 0);
}

From there, I knew I would need to use mask-composite or the non-standard -webkit-mask-composite to combine the masks in different ways.

Here is an initial attempt that won't work on Firefox. I'll leave an image:

These are the values I used:

• OR: initial. There's no need for a special value as the default is that they all will overlap. I didn't even need to add a mask-composite.
• AND: intersect. The applied mask will be an intersection of all the masks. In this case, the intersection of both circles.
• XOR: exclude. This one allows for two alternatives. For mask-composite, the exclusion can be achieved with exclude. But we could also use the xor value of -webkit-mask-composite... which kind of makes more sense in this case but, as mentioned above, is non-standard.

For the second row, I needed a third mask to occupy the whole container (and an additional one for the NAND!) I must admit, it is kind of messy:

• NOR: -webkit-mask-composite: destination-out. Because the mask that occupies the whole container is last, the pixels from the previous mask (equivalent to trick OR treat) are cleared, leaving the space outside the pumpkin with color.
• NAND: mask-composite: subtract. I overcomplicate this one with far too many layers (4), trying to keep it standard and with a single mask-composite value.
• XNOR: -webkit-mask-composite: xor. The irony. To create XNOR, we use the xor value but with the additional layer that will cause to "flip" the selection.

It was messy. Temani Afif and Ana Tudor —you should follow them on social media if you don't already, they are amazing at CSS—, chipped in and helped simplify the code and use the standard mask-composite property.

The result is below. It requires setting the masks for each cell, and indicating the mask-composite value inline. And while I was at it, I decided to expand the joke a little and include a few more logical gates (some of them required more than just 2 and 3 masks):

---

comiCSS version

Although it works fine as it is, I decided to make a shorter version that only uses the CSS standard for the CSS comic I publish (you can follow it on Medium, too!)

It only uses the logic gates generated with two masks and the standard mask-composite property, so it will work in all browsers. Plus, it showcases each value individually. Fun and educational (I hope).

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