Printing JPEGs

I'd welcome some advice - and I apologise for the detail.

I have met an odd problem when using my !Calibre application and it
seems to be centred on the SWI "JPEG_PlotScaled"

The problem is that - in some circumstances - when trying to print a
JPEG (small or large) the application/computer 'hangs' - and in such
a manner that it will then not respond to Alt-Break nor Ctrl-Break.

The odd bits are:

a) the problem *never* occurs on *my* desktop RPC (RO4.39, Printers
1.62). !Sprinters also works OK on this RPC.

b) the problem *always* occurs on my VRPC-Adjust (4.39) using
UniPrint with Printers+ 1.91a and also *always* occurs with !Sprinter
on this VRPC. The problem does *not* occur on this VRPC if using,
say, a PS driver 'printing-to-file' to the VRPC 'hard disc'.

c) If the JPEG is put into a drawfile and that is used instead in
Calibre, no problem occurs. (Calibre is designed to accept either
drawfile or JPEG graphics.)

d) The application - within the very well-established DrWimp printing
process following RO standards - uses only one small routine to call
SWI "JPEG_PlotScaled" and this routine is called both for displaying
and printing the JPEG. When the printing problem occurs the JPEG has
already displayed without a problem.

e) one other user has reported that he gets the same problem with his
desktop RPC using RO4.39 and Printers 1.90b4. (I am getting him to
check out !Sprinter.)

----------

I have referred to VirtualAcorn/RComp/Risc OS to try to get some
clues but nothing so far has emerged. (I have checked that all the
appropriate memory allocations in my VRPC are at least as large as
those in my RPC. In most cases the VRPC has much more memory. Making
the WimpSlot huge makes no difference.)

I seem to have isolated the problem to the above SWI call. I have
also confirmed that the input register values to the SWI are exactly
the same for both the display call and the printing call. (The JPEG
is loaded into DA prior to the SWI call. It makes no difference if
the JPEG is loaded into separate DAs for display and printing (more
desperation!).)

Further, if I set R3 to zero (i.e. no scaling) the problem does *not*
occur - although, of course, the size of the displayed & printed JPEG
is then not user-controlled.

So the problem - in the limited circumstances where it occurs - seems
to be focussed on *printing* a scaled JPEG (but *displaying* the same
JPEG from the same DA with the same R3 scale values is not a problem).

At the moment, with only two users reporting the problem, the only
significant common factor when the problem occurs appears to be the
Printers version....

Can anyone offer any thoughts as to what might be happening?

Even if you can't, I'd welcome any Calibre user telling me if they
have met the problem and in what set-up.

Fortunately, it is not a disaster because the drawfile route gives a
'get out of jail free' card, but I'd much prefer to cure the matter.

TIA

--
Regards from Ray Favre. Email at: <ray@xxxxxxxxxxxxxx>
Web site at: <http://www.rayfavre.me.uk/>
Tel: (+44) (0)1895 444410
.

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