how does Krita paint layers to the screen?

[Michael Thaler]

Hello,

I want to understand how Krita compose layers and paints them to the screen.  
Boudewijn pointed out that KisImage::renderToPainter paints the image. But 
this function doesn't to the actual compositing. Where does this happen? Can 
someone explain this to me? The reason I ask is, because I wonder if it is 
possible to create a text layer with kotext.

Greetings,
Michael