[OpenJDK 2D-Dev] X11 uniform scaled wide lines and dashed lines; STROKE_CONTROL in Pisces

[Denis Lila]

Hello Jim.

> So either it is always on the right side, always on the wrong side
> (i.e. just reverse the rotation in the math), or always on the right/wrong 
> side depending on the CWness of the join angle - which would be 
> reflected in rev...  No?

That's a good point. I've changed the test to simply if(rev) because
the normal we compute is on the left of the original vector
(omx,omy)-(mx,my). So, if the arc was counter clockwise no adjustment
was needed.

Regards,
Denis.

----- "Jim Graham" <james.graham at oracle.com> wrote:

> Right, but it seemed to me that if omxy was the "from" vector and mxy
> 
> was the "to" vector, that the computed mmxy should always be
> predictably 
> on the same side of it, no?  If it was on the wrong side then it 
> wouldn't be a random occurence, it must be related to the input data.
> 
> 			...jim
> 
> On 10/20/10 10:29 AM, Denis Lila wrote:
> >> Cool, but above I was also asking the same question about line
> 231,
> >> and you provided a lot of information about line 231 (and a test to
> verify
> >> it), but didn't answer if the test in line 231 also tracks rev the
> >> same way...?
> >
> > Oh, no, line 231 isn't mean to be related to rev at all. It just
> checks
> > to see on which side of the (omx,omy),(mx,my) chord the computed
> (mmx, mmy)
> > is.
> >
> > Regards,
> > Denis.
> >
> > ----- "Jim Graham"<james.graham at oracle.com>  wrote:
> >
> >> Hi Denis,
> >>
> >> One clarification:
> >>
> >> On 10/20/10 7:11 AM, Denis Lila wrote:
> >>>> When would the isCW test trigger?  Does it track "rev"?  What
> >> happens
> >>>> at 180 degrees (is that test reliable for the randomization that
> >> might
> >>>> happen when omxy are directly opposite mxy)?
> >>>
> >>> isCw is used for computing the arc bisector by testing whether
> the
> >> computed
> >>> point is on the side it should be (and multiplying by -1 if not),
> it
> >> is used
> >>> to compute the sign of cv in drawBezApproxForArc, and for
> computing
> >> rev.
> >>>
> >>>> The only reason I ask is
> >>>> because I think the sign of mmxy is probably controllable by
> >>>> understanding the input conditions, but this test should be safe
> >>>> (modulo if it really works at 180 degrees).  If it has failure
> >> modes at 180
> >>>> degrees then reworking the math to produce the right sign in the
> >> first
> >>>> place may be more robust for that case.  A test for this is to
> >> render
> >>>> "(0,0) ->   (100,0) ->   (0,0)" with round caps and then rotate
> it
> >> through
> >>>> 360 degrees and see if the round caps invert at various angles.
> >>>
> >>> I already did that. I drew 100 lines like the one you describe. I
> >> attached
> >>> the results. It never fails. It is still possible that there
> could
> >> be some
> >>> case where it fails, but this does prove that such a case would
> be
> >> very rare.
> >>>
> >>>> Also, line 256 - does that track "rev"?
> >>>
> >>> It does. I changed the test to if(rev).
> >>
> >> 			...jim