Hi,
I had posted a while back about wrapping the Poppler PDF library using QT
Jambi, so that
it could be used from Java. Although Poppler uses C++ Namespaces, I wrapped the
3 or 4
functions that I wanted in my own class, used the Jambi Generator and
everything was
great. At the time, it was mentioned that better Namespace support was coming
with 4.4 so
I figured I would wait until then to "properly" wrap the entire library
(without having to
also write my own C++ classes to wrap ever Poppler class that I wanted).
Anyway, I've now set out to write my own JNI code to do what I want, instead of
using the
Jambi Generator. Everything was working nicely until trying to transfer a
QImage from C++
to a Java/Jambi QImage. Back in February, Gunnar suggested stealing some logic
from the
generated Jambi code, in particular QPixmap::toImage():
jobject jimg =
qtjambi_from_object(env,
&image,
"QImage",
"com/trolltech/qt/gui/",
true);
This works -- almost. I get back a valid Java QImage object
(System.err.println(image)
prints something like [EMAIL PROTECTED]) but when I try to do anything
with it (like call image.width()), the JVM crashes.
Now, the image object (QImage) that I'm getting back is on the stack (hence the
address-of
&). If I make a copy of it on the heap (QImage *copy = new QImage(image)) and
then pass
that copy pointer directly to the qtjambi_from_object function (i.e. no
address-of
operator & since it is naturally a pointer) then it doesn't crash -- so long as
I don't
delete the copy pointer (which makes that a big memory leak). (creating a copy,
not
deleting it, but using the original &image in qtjambi_from_object DOES crash
the JVM (weird)).
Something else that is weird (though this may be a red-herring, i.e. luck) if I
construct
more than 1 QImage (in Java, i.e. QImage i1 = page.renderToImage(); QImage i2 =
page.renderToImage();) calling i1.width() crashes the JVM but i2.width() does
not! (i1
being the first QImage created this way) In fact, just the line "new
QPixmap().toImage()"
seems to prevent a crash. Through some trial and error, I tried inlining a
bunch of the
code from qtjambi_from_object and it seems that just calling the following one
line before
calling qtjambi_from_object prevents a crash:
resolveClass(env, className, packageName);
Thoughts?
Thanks,
-Adam Batkin
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