[Lazarus] Getting update rect/region in Windows

[Hans-Peter Diettrich]

Max Vlasov schrieb:

> Ok, another example. Imagine that two alpha png is merged and drawed on 
> the form on the fly.

Is that on-the-fly merging really necessary?

> And you drag a small window over this form. My 
> experience tells me that win32 will do great automatic job of narrowing 
> the final drawing of the bitmap to smallest rectangle possible, but my 
> internal procedures of alpha-blending can get this information only from 
> GetUpdateRect/GetUpdateRgn, otherwise every single pixel moving of this 
> window will lead to full alpha-blending of these bitmaps. ClipRect won't 
> provide this information

I'm not sure what you mean. When the dragged window also uses 
alpha-blending, then Windows (GDI) must do that job. Using GetUpdateRect 
IMO should not work, because BeginPaint restricts output to the ClipRect.

DoDi