What happens when a UI monitor is "loaded"?


I have been working on Qt/qml based UIs.

I used something like 'dynamic on requirement loading' of screens. (using a loader element)

Advantage: All screens need not load at startup, improves systems startup time.

Disadvantage : When ever a screen has to be loaded later, it takes time, and decrease in user responsiveness at that moment.

My question is, what is actually 'loaded' into the memory when I say, load a UI screen ?

I mean if its C++ code, I would understand it like some dynamic objects are being created. I cant visualize it in terms of UI screens ? Is it like the images I have used in making that UI are loaded into memory for different operations ?

Adding to the earlier question, what happens when I 'unload' a screen ?

Is the CPU requirement same for loading and unloading ?

There is very good and detailed explanation what exactly going on when declarative engine loading a qml file: