[Lazarus] Getting update rect/region in Windows

[Zaher Dirkey]

2011/5/22 Max Vlasov <max.vlasov at gmail.com>

>
>
> 2011/5/22 Zaher Dirkey <parmaja at gmail.com>
>
>> 2011/5/22 Max Vlasov <max.vlasov at gmail.com>
>>
>>>
>>>
>>> 2011/5/22 Zaher Dirkey <parmaja at gmail.com>
>>>
>>>>
>>>> 2011/5/22 Max Vlasov <max.vlasov at gmail.com>
>>>>
>>>>> Hi,
>>>>> I encountered a problem I don't know how to solve.
>>>>>
>>>>> In Delphi I used the following trick. In the WM_Paint before inheried
>>>>> call I got update region with successive calls to GetUpdateRect (to
>>>>> determine if it exists) and GetUpdateRgn afterwards. This allowed to get the
>>>>> correct region before BeginPaint is called (it validates the region so
>>>>> getting it after BeginPaint makes no sense).
>>>>>
>>>>> But in Lazarus WM_Paint handler already contains DC and also
>>>>> GetUpdateRect call is failed. As I understand, this is because the
>>>>> WindowProc from win32callback.inc already did BeginPaint and provided the dc
>>>>> for the following call to the control WM_Paint.
>>>>>
>>>>>
>>>>> Max Vlasov
>>>>>
>>>>>
>>>> Check Canvas.ClipRect
>>>>
>>>>
>>>>
>>>
>>> Zaher, thanks,
>>> but this is irrelevant, clipping rects and regions is just  the way to
>>> define canvas/device context limiting area until explicitly canceled. It was
>>> used by Delphi and (probably) Lazarus to implement TGraphicControl,
>>> component working almost as TWinControl but without window handles.
>>> ...
>>> Max
>>>
>>>
>> Not understand u, can u give us an example
>> Thanks
>> --
>>
>
>
> Ok,
> simple form, one button. The following code works in Delphi (press button,
> redrawing with Alt-Tab or by dragging some other window over this window).
> In Lazarus it always goes to 'failed'.
> My version: with Delphi vcl logic BeginPaint will be inside inherited, with
> Lazarus it already was before in the non-object WindowProc
>
> Max
> ...
>
> procedure TForm1.Button1Click(Sender: TObject);
> begin
>   { change Bounds to @ARect in Delphi since it's declared as PRect }
>   InvalidateRect(Handle, Bounds(0, 0, 100, 100), true);
> end;
>
> ...
>   private
>     procedure  WmPaint(var Msg: TWmPaint);message WM_Paint;
>
>
> procedure TForm1.WmPaint(var Msg: TWmPaint);
> var
>   ARect: TRect;
> begin
>   if GetUpdateRect(Handle, ARect, false) then
>   begin
>     Caption:=format('Update Rect is ok (%d, %d, %d, %d)', [ARect.Left,
> ARect.Top, ARect.Right, ARect.Bottom]);
>   end
>   else
>     Caption:='Update Rect is failed';
>
>   inherited;
> end;
>
>
In Lazarus i used
procedure Paint; override;

and

Canvas.ClipRect;

It is work for me as Hans-Peter said in his message.

If you ask about Rgn (Region), it more complected to work on all platforms,
i think it is not founded.

-- 
Zaher Dirkey
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