I'm making another attempt at writing a game engine, but I want to focus mainly on developing the runtime component, so I want to leverage existing asset creation and map editing tools as much as possible to avoid having to write my own offline tooling.
Is this possible to do, or should every engine provide at the very least an editor for positioning game entities and setting their properties? Can something like blender do all of this? It would have to allow me to create 2D menus, spawn points, camera paths (for cut-scenes, etc.), and basically everything else a game needs. How would I handle custom game objects with their own properties that blender doesn't know about? I will surely need to place objects on the map and tweak their properties. Can blender (or similar) allow you to add custom properties to game objects?
What would be useful is an open source (incl. data) 3D game I could examine whose assets can be viewed and edited using freely available, non-proprietary content creation tools. Then I could use the exact same content pipeline for my games but with my own engine runtime. ALL of the game assets would need to be editable with non-proprietary tools - not just the 3D models. I want a complete content creation solution, basically.
Is this realistic, or does writing one's own engine necessarily entail writing map editors and things too?
Thanks