What does this source code do?

[Ejaz]

1) What is the purpose of redraw window in this scenerio? Is it necessary for the child window approach to work?

It is trying to kick the particular window so that WM_SETTEXT message against the particular area (i.e. passed in rect), can be filtered.

I haven't used hooks for long time, therefore please check it at your end.

2) Only a small number of windows return any text from WM_GETTEXT. Is there another way? Some technique that DOES repainting on the screen?

Again, I haven't done this myself, but I think it will take more then simple WM_GETTEXT, especially when it comes to non-text static controls (such as images, icons etc). Check the remarks section for WM_GETTEXT in MSDN.

I would like to ask here is that what exactly you want to achieve here?