Re: Drawing pixels in win32 mode

Ulrich Eckhardt <>
Thu, 14 May 2009 11:56:29 +0200
Jack wrote:

While we can draw pixels and lines within WM_PAINT, I know there must be
ways to draw the stuff in other places...

Yes, but see below.

like within WM_CREATE?

I wouldn't count on that, since this is just initialisation and might not be
completely finished.


I saw nothing coming up the screen when I did that. But as I put the same
function inside WM_PAINT, everything went okay.... is it a constraint of a
typical Win32 application? Or I have just overlooked something...

Yes, you are misunderstanding the design of the win32 API. You don't draw
into an area that is stored but on screen. So, if another window covers
your target area, your drawings are erased. Now, if the other window is
removed and your window area is uncovered, the framework sends you a
WM_PAINT where you should redraw those uncovered areas.

If you draw anything but not in WM_PAINT, it wont be redrawn when you move a
window over it. So, to fix that, you must draw it in WM_PAINT, too, but
then there's no use for drawing outside that in the first place.

Just for completeness: there are valid applications for drawing outside. I
have a graphical display for some sample data which take easily two seconds
to render. I can't do that in WM_PAINT, so I stepwise draw it to a bitmap
in memory with a timer. In WM_PAINT, I only blit the bitmap to the screen.
However, the principle that I only draw _on screen_ in WM_PAINT still


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