Thanks a lot for your answer.
I am talking real-time rendering, not pre-rendered. But for purpose other than a game.
I am talking about realtime graphics for live productions and interactive/generative installations.
As such, the realtime graphic engine of a game engine fits perfectly as well as all the interactivity features, but in this particular field, we miss a way to display the realtime rendered scene outside of the game engine. Though this is not a purpose of a game engine hence the need of Syphon / Spout / NDI protocols and MIDI / OSC for data exchange and support for video capture cards for instance as gateways to bring video and controls from the game engine to other specialized software.
I know those feature are more of plugins as they don't concern game dev as such. Also i know this is not the direct purpose of a game engine, but demand is increasing really fast in this industry.
Was just asking as i don't develop games but interactive installations.
thanks a lot