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| Re: handles and native code [message #437976 is a reply to message #437973] |
Mon, 14 June 2004 15:48  |
 Ivan Markov
Messages: 61
Registered: July 2009 |
Member |
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e.gc.handle is of type HDC.
You are treating this HDC handle as HWND which is wrong.
You can instead just change drawDocument to:
JNIEXPORT jint JNICALL Java_drawDocument (jint myHDC)
drawMe((HDC)myHDC);
Or alternatively, you can try passing to drawDocument *not* e.gc.handle, but
e.gc.data.drawable.handle (whgich is of type HWND)
The first approach is more correct though, because e.gc.handle has some
niceties which GetDC(gc.data.drawable.handle) doesn't have, like correct
clipping rectangle, fgnd/bgnd colors, etc.
/Ivan
"Mark" <freiheit@speakeasy.net> wrote in message
news:cakeke$fdu$1@eclipse.org...
> Hi all...
>
> I have a need to use an existing C++ DLL that draws graphics onto
> a user provided HDC. I wish to encapsulate this drawing to a
> particular portion of the screen where the rest contain SWT controlling
> widgets.
>
> I wish to create a Canvas on a Composite, and provide its handle to
> the C++ code to do the rendering as in the following pseudo-code.
>
> - java -
>
> myComposite.addPaintListener( new PaintListener() {
> public void paintControl(PaintEvent e) {
> drawDocument(e.gc.handle);
> } });
>
> - C++ -
>
> JNIEXPORT jint JNICALL Java_drawDocument (jint myHWND)
> HDC myHdc = GetDC((HWND)myHWND);
> drawMe(myHDC);
>
> This does not work, and I am curious precisely why. It may have
> something to do with the native DLL not "owning" the handle passed in.
>
> If I use the examples provided in the
> "Create your own widget" article, I observed that the author
> creates a child window from their handle, thus...
>
> JNIEXPORT jint JNICALL Java_drawDocument (jint myHWND)
> HWND child = ::CreateWindowEx(....., (HWND)myHWND, ...);
> HDC myHdc = GetDC((HWND)child);
> drawMe(myHDC);
>
> Does indeed draw something. But it loses all context of the parent.
> That is, it appears to be drawing to the manager window, and is not
> constrained to the original Composite that I provided.
>
> 1) Is there some way I can draw directly to the Composite I provide?
> 2) Is there a better way in general to accomplish my goal?
>
> Thanks a bunch -- Mark
>
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