🚀 go-pugleaf

I've posted a problem with Canvas->CopyRect sometime ago. It seems I found
the reason of that problem. But still can't solve it  :-(

In my program, I'm using a WorkSpace (Bitmap) to apply all the graphic
operations (e.g. CopyRect). Then I use CopyRect to copy the updated area
from WorkSpace to a PaintBox (visible Bitmap). At the same time, I'm using a
OnPaint procedure which is copying the entire WorkSpace into PaintBox.
Everything seems OK when I was using TTimer to draw my WorkSpace.

Now I changed my program to use TThread to draw on the WorkSpace.
Unfortunately, it could happen that while the thread is drawing the OnPaint
procedure is called, i.e. the PaintBox is restored with an unfinished image.

Now I'm trying to use Semaphore (max value= 1) to fix it. I use
WaitForSingleObject() and ReleaseSemaphore() to enclose the codes of
modifying the WorkSpace and also enclose the OnPaint codes. I hope if
OnPaint is called and WorkSpace is busy OnPaint will wait until WorkSpace
Semaphore is released. But it seems there's no effect at all :-(

What did I do wrong? I also read something about EnterCriticalSection(), I
thought I don't need it because I'm usig only one flag, do I need it?
Any better solution?

Thanks
Phuoc Can HUA