🚀 go-pugleaf

It is hard to diagnose your problem without seeing yuor actual code.  But
offhand, it sounds like you are trying to draw directly onto the PaintBox
from your thread directly.  If so, then you shouldn't be doing that, as the
VCL is not thread-safe and can't handle cross-thread painting correctly.
Instead, you should be doing your thread-based drawing to a separate
in-memory bitmap that is properly protected by a synchronization object
(mutex, critical section, semaphore, etc), and then the thread can obtain
the lock to the bitmap when it needs to alter the bitmap, and then the
OnPaint event can obtain the lock when it needs to update the PaintBox with
the bitmap.  That way, only one is trying to access the bitmap at any given
time.


Gambit

"Phuoc Can HUA" <home+a+t+huaonline.com> wrote in message
news:3e90c1f3$1@newsgroups.borland.com...

> Now, when I move the main form over the form with the
> PaintBox very fast the image can't be restored properly. It looks
> like Windows can detect the 'invalid' area and only updates a
> small part of the PaintBox, although my procedure copies the
> entire image. That's OK. But the 'funny' thing is that the update
> segment sometimes appears at the wrong place, somtimes even
> somewhere on the screen (outside of the paintbox). Of course,
> sometimes it crashes as well :-(

"Remy Lebeau (TeamB)" <gambit47@yahoo.com> wrote in message
news:3e90fe9b$1@newsgroups.borland.com...
> It is hard to diagnose your problem without seeing yuor actual code.  But
> offhand, it sounds like you are trying to draw directly onto the PaintBox
> from your thread directly.  If so, then you shouldn't be doing that, as
the
Yes, the thread is drawing using several Canvas and copy the results from
the WorkSpace to PaintBox and this is running all the time. I had some
problems with Canvas before, until I use Lock/Unlock. I also tried to use
lock on PaintBox. But somehow the whole OnPaint routine stuck :-)

> VCL is not thread-safe and can't handle cross-thread painting correctly.
> Instead, you should be doing your thread-based drawing to a separate
> in-memory bitmap that is properly protected by a synchronization object
> (mutex, critical section, semaphore, etc), and then the thread can obtain
> the lock to the bitmap when it needs to alter the bitmap, and then the
> OnPaint event can obtain the lock when it needs to update the PaintBox
with
> the bitmap.  That way, only one is trying to access the bitmap at any
given
> time.
Haven't got all what you mean. Do you mean... the thread only draws on a
bitmap (Canvas?) without copying the results to the PaintBox. But how can I
display the results? Do I have to trigger OnPaint to refresh the image? Will
the OnPaint re-paint the entire image?

Currently, my OnPaint seems to be running 'wild'. As I mentioned, sometimes
it just draws on the screen across several windows.

Phuoc Can HUA


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My Homepage is my Castle

"Phuoc Can HUA" <home+a+t+huaonline.com> wrote in message
news:3e9107d2$1@newsgroups.borland.com...

> Haven't got all what you mean. Do you mean... the thread only
> draws on a bitmap (Canvas?)

Not a Canvas, no.  Well, yes, but not a standalone TCanvas, but an actual
TBitmap instead.  Or, since you're posting this in the .nativepapi group, a
call to CreatecomatibleDC(), CreateCompatibleBitmap(), SelectObject(), and
any drawing functions you're using.

> without copying the results to the PaintBox.

Not from the thread itself, no.

> But how can I display the results?

Put the bitmap where the PaintBox can get to it, and then it's OnPaint event
goes and grabs the current bitmap when needed.

> Do I have to trigger OnPaint to refresh the image?

Not directly, no.  However, your thread could Invalidate() the PaintBox
after rendering the bitmap.  Invalidate() wil force the PaintBox to redraw
itself when it is actually ready to do so, which will then trigger OnPaint
indirectly.

> Currently, my OnPaint seems to be running 'wild'. As I mentioned,
> sometimes it just draws on the screen across several windows.

I can't comment on that as you never posted your actual source code.  But
that sounds like a symptom of logic errors in your own code, or you're at
least not clipping the image first before drawing it so it doesn't go out of
the boundaries of the area of the PaintBox ou want to draw in only.


Gambit

"Remy Lebeau (TeamB)" <gambit47@yahoo.com> wrote in message
news:3e91b72c$3@newsgroups.borland.com...
> Not a Canvas, no.  Well, yes, but not a standalone TCanvas, but an actual
> TBitmap instead.  Or, since you're posting this in the .nativepapi group,
a
> call to CreatecomatibleDC(), CreateCompatibleBitmap(), SelectObject(), and
> any drawing functions you're using.
I was thinking to post it in the graphic group. But I thought this is much
more a problem with the thread. Thanks for your alternative solution. I'm
going to try it.

> I can't comment on that as you never posted your actual source code.  But
> that sounds like a symptom of logic errors in your own code, or you're at
Not that I want to keep my codes secret. I don't have my codes here (in the
office). Next time I will make sure I've got the latest copy here.

Phuoc Can HUA