[Lazarus] Getting update rect/region in Windows

[Hans-Peter Diettrich]

Max Vlasov schrieb:

> - There are some functions, for example region-related in windows that 
> nevertheless process full job even if the area the developer is drawing 
> is not included in the window update region
> - There are internal off-screen manipulation so the developer himself 
> have to do the job of avoiding extra processing so needs to know what 
> the update region is .

I use to restrict expensive painting to the ClipRect. The entire 
painting has to be organized into kind of "objects", which reside in 
distinct parts of the entire canvas - just like controls reside in 
distinct parts of the client area. Before retrieving the entire painting 
information, I get the object's rectangle and check whether it 
intersects with the ClipRect. If not, painting is skipped for that object.

DoDi