Thread by @delaneykingrox

Quick #gamedev #gameart trick.
When you use the alpha clip method of transparency it is binary- on/off. You either render the pixel, or you skip it.

However, your alpha channel is not binary. It is a float from 0.0 to 1.0.

This gives you a nifty trick...

See, to convert the alpha channel to on/off you set a mask clipping value. A value of 0.5 basically says only draw a pixel if the alpha is 0.5 or higher.

What that means is you can assign different values for different parts of your texture, and use the mask clipping value to reveal them bit by bit, or randomise them.

Say, a short moustache, a long moustache, a goatee and a full beard, all using the same texture.

So the alpha would be something like this.

(Alpha value)
(0.0) no beard.
(0.25) small moustache.
(0.5) full moustace.
(0.75) goatee
(1.0) full beard

As the clip value goes up they will disappear one by one.

This trick can also be used for dissolving characters. You can bake the models vertical world space value into the alpha, highlighting bits that you want to linger... like skeletons :)

It's a classic technique that can be used in many ways, and I am still coming up with things that leverage this trick.
Remember at the end of the day, textures are just arrays of numbers- red, green, blue and alpha are just four grids of values from (usually) 0 to 1.

You can use that data in a heap of ways... I have even seen object animations stored in textures as you can store positions in colours (r,g,b = x,y,z).

A classic alpha mask trick is to take all the posters on a wall and store each one as a different value on the alpha- anything above, say 0.05 is solid, so that gives you all that data above to use for stuff like masks.

You can then say "okay, anything in the alpha from 0.06 upwards, tint color A- anything from 0.25 upwards, tint color B, and anything above 0.5 tint color C.

You can then randomise those colors with a script.

And that means the poster texture is different each time you use it.

One last trick- is "super black" clipping.

This uses your color texture map WITHOUT an alpha channel to get the exact same results.

You make the texture slightly brighter than black in photoshop, then paint out the bit you want transparent pure black (0,0,0)

In the shader, you take the colour output for, say, red. And you step this so anything above 0.01 is white, everything below is black. Plug this into your opacity mask.

Voila. Alpha clipping with no alpha channel.

Now you sure ensure that your values are enough that Mip mapping won't screw this up, but on the whole it works pretty good for dark rimmed objects- so if you use cartoon shaders with inked edges, super black is a great saving for alphas.

Okay, that's two tricks and I have to sleep now.

As always, I appreciate if you shout me coffees for my time here...

ko-fi.com/dellak

And my forthcoming book will have this stuff with sexy diagrams and example renders :D