This looks like a job for
Superman Connected Textures Mod (CTM), which is included in OptiFine. If you haven't already, go ahead and download the latest version of OptiFine before you continue reading this.
In order for this mod to work, you'll have to create three
.properties files; one for the side texture, another one for the top texture and one for the bottom texture. The names of the files doesn't really matter, but it's good to know what the different files are used for.
After that we need to add textures for the connecting slabs but since I don't know how many images I can add to this answer, I've decided to merge all textures as one image so you'll have to split them up in nine 16×16px PNG images yourself. Make sure to name them according to the table below in order to make everything work out.
100.png | 101.png | 102.png
103.png | 104.png | 105.png
106.png | 107.png | 108.png
Now we have to create a resource pack and add some folders where all these files and images should be. In the resource pack, open the
minecraft folders, then you have to create a new folder called
mcpatcher. Inside this new folder, create another folder named
ctm. And inside this folder, you must create yet another folder which you name
.properties files and images to the
default folder. If done correctly, you should have this folder structure:
| - minecraft/
| -- mcpatcher/
| --- ctm/
| ---- default/
When you start Minecraft, go to
Options -> Video Settings -> Quality and set
Connected Textures to either
Fancy and apply your newly created resource pack. When you are done, it should look like this:
Edit: Added a
.properties file for the bottom texture of the slabs.
Edit 2: Added the
metadata parameter for the files so the texture is only applied to top and bottom stone slabs.