I was wondering how tough it is to create a Drag&Drop engine, not necessary for gaming, but maybe for websites or even normal mobile apps, what language does it require and how will it export to platforms like IOS or Android. The reason I'm asking is because recently there have been many many Drag&Drop engines that do various stuff, even something like Illustrator or Photoshop could be considered a drag&drop.

I was wondering how tough it is to create a Drag&Drop engine,

There's no specific thing called a "drag and drop engine", because dragging and dropping isn't complex.

Can you draw an image at an x/y location?
Well, when "dragging" something, you just make the x/y change based on the x/y location of the mouse (or a finger on a touchscreen).

There's a few other minor details, but that's basically it.

It's everything else unrelated to the dragging and dropping that'll take time to write. Have you written any computer programs before?

what language does it require

Any language that can receive the location of the mouse/finger, and any language that can draw an image to a specific location onscreen.

and how will it export to platforms like IOS or Android.

Export what to iOS or Android? That's an different question, it's unrelated to dragging and dropping.

The reason I'm asking is because recently there have been many many Drag&Drop engines that do various stuff, even something like Illustrator or Photoshop could be considered a drag&drop.

Yep, ever since the very first mouse was created, people have been creating applications with dragging and dropping (at the very least, since the first Macintosh). The mouse was created 45 years ago (30 years for the Mac), and many applications and OSes have supported it for decades. It's nothing special.

Maybe he's referring to dragging and dropping things from outside the app onto the app? But I don't think that really applies for phones. And it's not all that difficult, just requires handling messages from the OS, which would obviously be platform specific, but could be abstracted to work on every platform that has drag and drop.

Maybe he's referring to dragging and dropping things from outside the app onto the app? But I don't think that really applies for phones. And it's not all that difficult, just requires handling messages from the OS, which would obviously be platform specific, but could be abstracted to work on every platform that has drag and drop.

If that's the case, I'd use a library that wraps native OS messages.

I'm not familiar with Android/iOS, but Qt does this excellently for Window/Penguin/Macintosh, supporting drag and drop mimedata within and between applications, and between the app and the OS. I've implemented it in my own application, and it works very well and was very easy to implement (if you already know how to program).

Don't know if OP's question is this or extends to this, but could a generic app creator drag and drop include visual-implementations and actions (not just resource for designers) that have modification parameters and also auto-generates code? Such that you are not just moving things to different locations, you can actually be more creative?

I guess the difficulty with such drag & drop could be interfacing with APIs such as the camera

Yes, there are things like drag-and-drop scripting, drag-and-drop level editing, drag-and-drop shader-creation, and so on. Personally, I think these tools best work at higher levels of abstraction to get the rough work knocked out quickly, and then diving deeper in (behind the tools, at a lower level) to add/tweak the fine details.

They don't enable you to be more creative, they just make the tools easier to use, and possibly (depending on the interface) let you create things faster.

They may actually hinder creativity if they prevent you from going lower level, but if they exist in addition to going low level, then they can definitely be a convenience (and reduce the learning curve) if they are well-designed.