In a first time I set the background of the underlaying panel to black
but this is not necessary and now it is clBtnface.
The sky chart is first draw to a Tbitmap. In the drawing component
onPaint I just draw this bitmap to the canvas along with temporary
drawing if any (selection mark, ...).
Using a Timage there is a lot of flicker, when resizing, but also when
drawing a temporary lines directly with pen.mode=pmXor.
With the drawing component there is no problem.
This is unfortunately not the most simple application to use as an
example but if you want to look at the source code it is at:
http://svn.sourceforge.net/viewcvs.cgi/skychart/trunk/skychart/
The drawing component is in pu_chart.pas.
Patrick
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