From what I get up to now, you want to use unity's editor to create your scene - then get the output file and read it so you can use it in another engine. To do this you'll need to know the structure of a unity scene(?) file, and be able to make sense of each structure in the unity file and convert it to something that makes sense in your engine.
No, I don't want to use unity scene's editor to set where level objects are (like start point, obstacles position, bonuses... so essentially data, anything that isn't game logic).
I'd like to do something like:
There isn't really such a thing as an engine independent way of building levels.
There hardly even is such a thing as a game independent way of building levels.
Most use some set of custom tools, or plugins/exporters to existing tools (such as the unity editor or maya, or blender, any of the tile editors out there, etc) to build levels for that specific game, and building the tools is part of the work needed to make the game.
Or, if it is a small simple game, there might not be an editor at all, all set through code, or even generated.
Or, just an xml file written in any text editor.
Keep in mind any representation of a "thing" in a game has to be assembled from some data.
For instance in a 3d engine if you walked around in an FPS environment all the walls, the ground, any object you can see is just defined as vertices at some point. At a basic level you can do this by hand, you literally set the buffers with code and then let the library render them out.
Thinking at a basic level you literally could build a large scale game doing nothing but typing out tens of millions of lines of code to set vertices and build models, but of course we don't do that because it would be horrendously clunky and a nightmare to do. The alternative is to use reusable code that can parse data to create the vertices. For instance we could have a simple text file with nothing but vertex coordinates typed one line after another, and then just create a small bit of code to load each set in a loop, instead of having to type all that code out each time we just use a simplified system to load it for us.
That is really all it comes down to, we move the data into files instead of code, we create tools to generate those files automatically with things like level editors or modeling software. What matters is translating the data from the files it resides in, into a form the engine can work with. For that reason there is no "standard" for level data. There are popular ones, for instance some engines just use standard modeling formats for their level geometry, and then they load extra files with data that describes dynamic objects, or what have you.
Basically it is all highly dependant on what the engine/game has been designed to work with.
Ok you two get the point.
Yeah an XML file would be what I need but actually I can't write it with a text editor! I wouldn't see the results.
Also, I think that it would be a waste of time making a GUI to set objects places...
I think I will write a little plugin for blender or photoshop (So I won't have to make a GUI) that export the project in a file XML formatted for my game and I'll read it with a parser like you said.
I've seen that there is a good tile editor but I think that I can't use it since my game's objects aren't tiled and loading them would be very slow for what i need.
Thank you all!