I am using Adobe Photoshop with the NVIDIA Texture Tools Plugin, which can be found here:
I am not going to go into detail on how to use Photoshop. So I am starting off with one of the first images I found on google. I also added some guides in the center and border of the image which will help me snap layers to the right position later on
As you can see the image is a bit dark along the edges, which means it won't work that well as a tiling texture: I fixed that by simply duplicating the layers, doing an offset filter and masking out the dark spot (see layers)
Now since usually textures in SC2 are angeled at 45°, I collapsed everything down to 1 layer, rotated and scaled it down (using the snaps) and duplicated the layer 4 times, moving one into each corner using my guides.
When done, feel free to collapse layers once again.
Now that the diffuse texture is done, I am creating the specular map, withing the alpha channel. (RGB = Diffuse, Alpha = Specular). Black = 0% reflection, white = 100% reflection and so on. I simply adjust the levels to get some contrast and make it darker overall, so it doesn't look like some shiny wet material when lit.
When done, Save as *.dds. Chose DXT5 in the dialogue to include our alpha channel.
Now for the normal map, I am going to use the NIVIDIA normal map filter, which can be found among the filters after installing the plugin. I used the RGB channels as input, with a range from 0-4. You might have to fiddle around with the settings to see which gives you the best result.
Blizzard kind of has their own normal map format, which requires us to make some modifications to the one we generated. What we do is create an alpha channel, copy the Red channel into the Alpha channel. Then fill the Red channel with 100% white, and the Blue channel with 100% black. This will give us some orangeish texture.
Once again, Save as *.dds, with DXT5.
Now off to the SC2 editor! Within the desired map, open the import dialogue, import the diffuse(+specular) and the normal map. Save your map.
Now in the data editor, go the the Terrain Textures tab. There we duplicate a similar texture. It's a bit quicker than creating a texture entry from scratch, as it includes additional information, such as which doodads to use when you generate foliage on that texture and the physics material.
Replace the diffuse and normal maps with the ones we just made. Ideally, you should have also made an editor (preview) icon, and name everything properly, which I was too lazy to do
When you have done all that, you can go to the Terrain Type tab, replace a texture in the tileset with the one we have just created, and reapply the terrain type in your map settings. You're now able to paint the new texture on your map!
HF & GL creating your own textures!