[OpenJDK 2D-Dev] Corner case drawing wide lines of zero length

[jon.vanalten at redhat.com]

Hi,

I am new to this list, hopefully it is okay that I post a potential fix to a very minor rendering bug.

I've been looking at a bug reported downstream at IcedTea:

http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=383

To summarize, if a line is drawn via Graphics2D.drawLine() of zero length but thickness greater than 1, the endcap decorations are not rendered.  This is because the sun.java2d.pisces.Stroker class ignores such line segments.  This is ideal in most situations drawing complex shapes, but when such a line segment is the entire shape the end result nothing at all is rendered.  The closed-source Sun JDK implementation does render endcap decorations in this case, and the documentation of the BasicStroke class related to this suggests that they should be rendered.

I've put together a (possibly straw-man) fix.  Please do pick it apart, I have never looked at the graphics implementation before trying to tackle this bug.  I basically add a boolean to indicate that the finish() step should be taken if *any* lineTo() call has occurred, and in the finish() step detect if there are any segments and if no manually draw in the caps (while allowing normal behaviour in other cases).

See webrev at:

http://icedtea.classpath.org/~vanaltj/webrevs/2d/zeroline/webrev/
(or download)
http://icedtea.classpath.org/~vanaltj/webrevs/2d/zeroline/webrev.zip

Your comments are appreciated.

cheers,

jon