At the end of my last log i was going to join all the small pieces that comprise each rock, so i could create a backface for the (big) rock.
Turns out that joining the pieces by welding their intersecting faces (turning them into a single mesh) bumped up the vertex count way to much; much more than i thought i could then remove, from the leftover triangles that would be created inside the mesh.
So, small pieces were kept separated and unwelded.
But it felt cheese to add backfaces to each individual piece so i stitched the pieces together just to create an edge around the entire rock, so i could then create a single bottom/back face.
Proceeded to do this for all the rocks i've used in the project.
Fully optimized? No. There's quite a few loose faces inside each mesh i can remove, if the map lags, so that's one optimization i can do.
I will also try, at some point, the Decimate modifier, in Blender, which "allows you to reduce the vertex/face count of a mesh with minimal shape changes".
So that's that, for Blenderland.
With the newly created backfaced rocks exported from Blender, replacing all the rocks on the map is a matter of just selecting them all at once in the library, and choosing their replacement counterparts.
Added the texture to the material file, which is shared throughout all the different rocks.
And they're back to look how they looked before.
Except, the sun doesn't shine through the rocks anymore. So, success.
An update to the art style: the rocks' texture now looks much more pleasing to look at.
A bit cartoony but i think they'll blend nicely with the game's assets.
Now, the whole idea of the backfaces was so that the sun didn't shine through the front texture. What i will do now is add the rock texture to the backfaces, to do some optimization; Instead of adding another rock in front, to hide that backface, i'll add a UV map and texture the backface.
This way, there's less objects on the screen, and, if the backface texture is only seen from afar, the player shouldn't notice it's a flat face.
And that's the rock/sun issue fixed!
Moving onto some more environmental design.
