[OpenJDK 2D-Dev] RFR JDK-8184429: Path clipper added in Marlin2D & MarlinFX 0.8.0

Laurent Bourgès bourges.laurent at gmail.com
Thu Aug 31 07:43:56 UTC 2017


FYI I am working on a more general clipper for filled shapes (only non zero
winding rule) that ignores useless segments on left / right sides but
leaves the path closed for filling primitives.

It is more tricky... to handle turning points (corners) but I think it
could be applied later to the Stroker case to avoid opening the path (and
require ClosedPathDetector).

Should I look at the Area class that performs such clipping but is known to
be extremely slow ? If you think it is useful, I could optimize it as I did
in Marlin (array caching...). What is your opinion ? Is Area used in the
java2d pipeline ? That would improve the overall performance.

PS: I wonder if curves should be subdivided at inflexion / root points in
this (too) basic fill pipeline to improve cubic / quad accuracy (as it is
the case in Stroker) and have monotonic curves.
I studied AFD accuracy (inc/dec thresholds) but did not try curve
subdivision to guarantee the special point accuracy (cups...)

Hope you will have time soon to look at the webrev, your feedback may help
a lot.


Le 29 août 2017 2:58 AM, "Jim Graham" <james.graham at oracle.com> a écrit :

Hi Laurent,

On 8/28/17 2:09 PM, Laurent Bourgès wrote:

> Hi Jim,
> Thanks for your comments, it helped refining the webrev.
> Here are my answers:
> 2017-08-26 2:22 GMT+02:00 Jim Graham <james.graham at oracle.com <mailto:
> james.graham at oracle.com>>:
>     [D]Dasher.java - why the changes from (firstSegIdx > 0) to
> (firstSegIdx != 0)?
> As firstSegIdx is initialized to 0, I prefer testing (firstSegIdx!= 0) as
> it looks more obvious.
> For me, (firstSegIdx > 0) indicates that the sign has a particular meaning
> and that firstSegIdxmay be negative.

Interesting, I'm used to != 0 being only used in contexts where the value
might have some specific reason for being negative, but I can see why you
did that.

    [D]Stroker.java, line 196ish - why are ROUND treated differently.  You
> have a question on that as well in a comment.
> I found the answer: C = 4/3 * (SQRT(2) - 1) is used to compute the control
> points (cubics) to approximate a circle. I fixed the constant estimation
> according to the math formula.

The control points don't control how far the path gets from the line,
though - that measurement is arbitrary compared to the clipping operation.
The correct distance from the vertex to the edge of the drawn path is lw/2.

I agree your new rules.
> I fixed the (D)Stroker init() methods according the latter rules and
> tested again.

Looks good.

Probably I should write a new Clip test rendering Z shapes with all  (cap /
> join) combinations and their bounds aligned to the Stroker's outside clip
> rules.
> Here is an updated webrev (Marlin2D only):
> http://cr.openjdk.java.net/~lbourges/marlin/marlin-080.1/
> PS: I can send you an updated MarlinFX patch (when you need it).

Not yet until I've had a chance to review the guts of the algorithm.  So
far I've only looked at a few boundary changes.  I'll get to that soon...

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