[OpenJDK 2D-Dev] More incompatibilities

Roman Kennke roman.kennke at aicas.com
Wed Mar 11 09:57:35 UTC 2009


so what happens now with this patch and the others? Should I enter them
into Bugzilla, so they don't get lost? Are they already in the process
of beeing integrated?


Am Dienstag, den 03.03.2009, 16:17 +0100 schrieb Roman Kennke:
> Hi there,
> > 4. StrokeShapeTest: createStrokedShape() behaves differently.
> It turns out that there is an arithmetic overflow here. The pisces
> stroker does a stupid thing here. First it initializes the
> scaledLineWidth like this:
>         this.scaledLineWidth2 = ((long)transform.m00*lineWidth2);
> which is infact wrong, because in fixed point arithmetics you need to
> apply >> 16, because the decimal moves.
> However, in another place it uses this factor like this:
>                 dx = (int)( (ly*scaledLineWidth2)/ilen >> 16);
>                 dy = (int)(-(lx*scaledLineWidth2)/ilen >> 16);
> which makes it ok in the end. The only problem is, that we start with an
> incredibly large number, then multiply another incredibly large number
> and _after_ that (when the overflow already occured) do the >> 16. The
> patch moves the >> 16 to the initialization of scaledLineWidth, which
> makes it clearer, more correct and even a tad faster, because we do the
> second calculation at least 2x.
> Of course, the real fix here would be to turn the whole implementation
> into floating point. This particular testcase is fixed by this patch,
> and the 'range of correct behaviour' is much large now, but if you deal
> with very large numbers in your shapes, then you will get trouble again.
> /Roman
Dipl.-Inform. (FH) Roman Kennke, Software Engineer, http://kennke.org
aicas Allerton Interworks Computer Automated Systems GmbH
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