I'd like to know what exactly is the resolution of the splatmap for the terrain textures (assuming EE uses splatmaps)...

I reckon you can have multiple textures per heightfield, each with an amount of contribution to the resulting combined texture... But the resolution of the splatmap is one pixel per heightfield.

How does the engine achieve the smooth transitions from one texture to another? Didnt seemed confined to heightfield Borders...

I try to set the terrain texture from script, therefore i need to know what possibilities i have here...

EDIT: I found another thing I could no figure out:

Area(C VecI2 &xz, Ptr grid_user);

What exactly is the grid user here? Is it just a "lock" object to prevent multiple objects accessing the area at the same time? Is it something different?

EE does not use splatmaps, it stores material data per-vertex

you should not call the Area constructor manually, you're doing something wrong. grid_user is custom user pointer, usually set to pointer to the World object containing the area.

Is there any good tutorial, classfile or wiki page where I could get an idea how to access the Area / Heightmap data, and possibly even set the material in the code?

I have trouble figuring it all out, and there is a very good possibility that I try to it completly wrong

EDIT:

Could someone with the knowledge point me in the right direction? I'm really lost how to use this functions and the materials in the editor code, a good example would be highly appreciated!

How do I get access to materials, how to load them, to use for Heightmap.setMaterial?
How do I get access to the heightmap in the Editor code? Do I need to access the heightmap over the Area, or is this part hidden somehow by a clever function from wich I can just access the complete heightmap?

there is already tutorial on how to process areas in the "customizable world editor" source code in the company license.