Move parent platform window

[Nuxar1]

The idea of this new flag is to create an imgui window the size of the parent Windows window and then to redirect movement to it. This allows for very easy creation of simple apps with a UI. This only works on windows.

The result:

Now making the windows window transparent you can get something nice looking like this:

[ocornut]

Hello,

I understand why you may want this, but this makes zero effort at acknowledging the multiplatform-ness of dear imgui, so that's not something we can merge.

I first suggest you have a look at Multi-viewports in the docking branch. Even though this doesn't do exactly the same thing nor this way, it tend to covers similar needs.

I think we will/should provide this feature perhaps even without multi-viewports and should aim to come up with a suitable design.