[Lazarus] Optimize DBGrid speed

[Hans-Peter Diettrich]

Petr Kristan schrieb:

> In the beginning of Grid paint is Canvas.GetClipRect called to obtain area
> which wee must redraw. This function directly calls WidgetSet.GetClipBox.
> I find out difference betwen Win32 and gtk2 bahaviour of this func.
> 
> In gtk2 TGtk2WidgetSet.GetClipBox returns previously Invalidated area
> (through DC.PaintRectangle = PS.rcPaint retrieved in BeginPaint)
> 
> But in win32 directly calls Windows.GetClipBox, but this func returns
> whole grid area. Do not takes account on invalidated area retrieved in
> BeginPaint.

It may be a bug in the Win32 widgetset, invalidating the entire control 
area instead of only the affected cell, *or* some special handling of 
invalidated areas by Windows. I remember that Windows used to extend the 
UpdateRect to include *all* invalidated parts of the DC. This can lead 
to a big update area, when a single bit at the top left and at the 
bottom right of the DC was invalidated. This may have changed in the 
meantime, though.

DoDi