Mo Glass is a Minecraft mod that adds glass stairs and glass slabs, including stained and tinted glass variants. They look great in any build and connect seamlessly with vanilla glass blocks. The mod is available for many different Minecraft versions, including snapshots.
(This assumes that you are using Windows with Eclipse and Java Development Kit 21 already installed.)
Clone / download the repository.
Run these two commands in PowerShell:
./gradlew.bat --stop
./gradlew.bat genSources eclipse
In Eclipse, go to Import...
> Existing Projects into Workspace
and select this project.
Both the stairs and the slabs are see-through in the same way as vanilla glass blocks. You can place multiple stairs, slabs and full blocks next to each other and they will look like a single piece of glass.
Slabs and stairs made from tinted glass will block light if you place them without any air gaps, or let the light through if there is a gap.
Before I started making this mod, I always thought that Mojang just forgot about these blocks, or that they were too lazy to add them. But now that I've added these blocks myself and spent many hours to get the transparency to work, I think I finally understand why Mojang didn't bother. Minecraft's stairs are surprisingly complex blocks and they were never meant to be made transparent. Slabs might be easy enough, but I think if Mojang added those then people wouldn't stop asking for the stairs. And glass stairs are an absolute nightmare to make.
Stairs can be placed facing North, East, South or West, they can be upside-down or right-side-up, they can be straight or curved in one of four different ways and they have six faces that may or may not be transparent, depending on what block is next to them. But here's the catch: On each of those six faces, there could be another block of glass stairs that can also be placed facing North, East, South or West, upside-down or right-side-up and either straight or curved in one of four different ways. And then of course, on each of the six faces there could also be a non-transparent block, a regular glass block or a glass slab that is either placed on the bottom half, top half, or is a double slab.
In the end, there are 10800 possible scenarios that need to be accounted for just to calculate transparency of glass stairs. But then you also have to calculate the transparency of glass slabs (810 possible scenarios) and adjust the transparency calculation of regular glass blocks (270 possible scenarios, or 258 more than before).*
That's a lot of effort just to add two new blocks to the game - and a lot of opportunities for new bugs to sneak in. That, I think, is why Mojang didn't bother.
So far, all connected textures mods that I've seen only seem to work on full blocks. They don't generate connected textures for stairs or slabs, which makes using them with Mo Glass impossible.
It's not that Mo Glass doesn't have support for connected textures, it's that connected textures mods don't have support for Mo Glass (or any other mod that adds stairs/slabs).
This might change one day as people make new mods all the time, so do let me know if there is a connected texture mod that supports stairs now. I'd be happy to add the extra texture files needed (if any) to make that work with Mo Glass.