Sorry, wrong patch. Here it comes.
/Roman
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
Haid-und-Neu-Straße 18 * D-76131 Karlsruhe * Germany
http://www.aicas.com * Tel: +49-721-663 968-48
USt-Id: DE216375633, Handelsregister HRB 109481, AG Karlsruhe
Geschäftsführer: Dr. James J. Hunt
diff --git a/src/share/classes/sun/java2d/pisces/Stroker.java
b/src/share/classes/sun/java2d/pisces/Stroker.java
--- a/src/share/classes/sun/java2d/pisces/Stroker.java
+++ b/src/share/classes/sun/java2d/pisces/Stroker.java
@@ -181,7 +181,7 @@
Transform4 transform) {
this.lineWidth = lineWidth;
this.lineWidth2 = lineWidth >> 1;
- this.scaledLineWidth2 = (long)transform.m00*lineWidth2;
+ this.scaledLineWidth2 = ((long)transform.m00*lineWidth2) >> 16;
this.capStyle = capStyle;
this.joinStyle = joinStyle;
this.miterLimit = miterLimit;
@@ -243,8 +243,8 @@
if (ilen == 0) {
dx = dy = 0;
} else {
- dx = (int)( (ly*scaledLineWidth2)/ilen >> 16);
- dy = (int)(-(lx*scaledLineWidth2)/ilen >> 16);
+ dx = (int)( (ly*scaledLineWidth2)/ilen);
+ dy = (int)(-(lx*scaledLineWidth2)/ilen);
}
} else {
double dlx = x1 - x0;
