Just downloaded, fantastic resource, thank you!
I was able to correct the walls. Long story short, the pointer values for things like My_texture_front were actually negative, so the "if My_texture_front > 0" would be false whether or not the texture was there.
Change:
- OBJ_3D_Box_Only_Sides: Draw lines from "if My_Texture_xxx >0" to "if My_Texture_xxx != 0"
- OBJ_3D_Box_Only_Sides: Create lines 42, 105, 167, and 229 the same way
- OBJ_3D_Box_Only_Sides: Room End lines the same way