[Lazarus] Drawing on MAC using GetDC

[Mattias Gaertner]

Torsten Bonde Christiansen <tc at epidata.info> hat am 7. September 2012 um 11:00
geschrieben:

> Hi List
>
>  I am currently trying to improve on the ported version of jvRuntimeDesigner
> component (available at SF here
> <http://sourceforge.net/projects/jvruntimedesign/> ),
>  but I am having a hard time getting it working correctly on a MAC with the
> Carbon widgetset.
>
>  More specifically the component uses a GetDC(..) (GetDesignerDC(..) on
> linux/windows) to retrieve a device
>  context to draw to, using regular canvas. But where on GTK2 (linux) and
> Windows the drawing goes well and
>  is fully visible, nothing happens on MAC.
>
>  My research have lead me so far, that I think the problem is that component
> has not system DC, but instead
>  is assigned an empty DC.
>
>  I have practically no experience in programming directly to MAC and I have no
> clue what to look for, so any
>  help would be appriciated.
>

You can paint *only* during the OnPaint event on Mac.

For the designer paint in the Paint event of the form:

  DesignerDC := GetDesignerDC(Form.Handle);
 ...draw...

  ReleaseDesignerDC(Form.Handle, DesignerDC);


Mattias