[OpenJDK 2D-Dev] Various fixes to pisces stroke widening code

[Denis Lila]

Hello.

And, I just finished it. At least it compiled successfully. I'm sure there 
are a few runtime bugs. I'll try to have a webrev out by today.

Regards,
Denis.

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

> Hi Denis,
> 
> float operations are pretty fast and they are usually done in a
> separate 
> part of the processor so the compiler can schedule a lot of
> bookkeeping 
> instructions to run in parallel with waiting for the results of the FP
> 
> instruction.  In the end, they often end up being "free" if there are
> 
> enough bookkeeping instructions (branches, fetching data, etc.) in 
> amongst the data.
> 
> Given how many alternate instructions you are pointing out for the
> fixed 
> point code it would be very likely that this would be a "win".
> 
> The main reason that Pisces is implemented heavily in fixed point is 
> that it was originally written for the mobile platform where there are
> 
> no FP instructions.  We don't have to worry about that on the desktop
> 
> (any more).
> 
> I strongly support you converting things to fp if you want to do
> it...
> 
> 			...jim
> 
> On 7/12/2010 8:05 AM, Denis Lila wrote:
> > Hello.
> >
> > Is it ok if I do this? I already started working on it on Friday.
> > I think I should be done by tomorrow.
> >
> > But yes, I agree that we should convert to floating point. As for
> > performance, there's also the fact that right now we're trading
> > one double multiplication for 2 casts to long, 1 long
> multiplication,
> > 1 bit shift of a long, and 1 cast back to an int. I don't know much
> > about how these are done in hardware, but it doesn't seem like
> they'd
> > be faster than the double multiplication.
> >
> > As for large coordinates, there's a bug report about it (one not
> > reported by me :) ) here:
> https://bugzilla.redhat.com/show_bug.cgi?id=597227
> > I submitted a matching bug report on bugs.sun.com (ID 6967436), but
> I
> > can't find it when I search for it.
> >
> > Denis.
> >
> > ----- "Jim Graham"<james.graham at oracle.com>  wrote:
> >
> >> Sigh...
> >>
> >> Pisces could really stand to upgrade to floats/doubles everywhere,
> for
> >>
> >> several reasons:
> >>
> >> - FPU ops are likely as fast if not faster on modern hardware due
> to
> >> parallel execution of FP instructions alongside regular
> instructions.
> >>
> >> - Don't have to worry about getting coordinates larger than 32K (I
> >> don't
> >> think this is well tested, but I imagine that Pisces will not deal
> >> with
> >> it very gracefully).
> >>
> >> - Lots of code is greatly simplified not having to deal with the
> >> semantics of how to do fixed point multiplies, divides, and
> >> conversions.
> >>
> >> I meant to do this during the original integration, but I wanted
> to
> >> get
> >> the task done as quickly as possible so that we could have an open
> >> source alternative to the closed Ductus code so I left that task
> for a
> >>
> >> later update.  But, now that a lot of work is being done on the
> code
> >> to
> >> fix it up, it might be better to do the float conversion now so
> that
> >> the
> >> maintenance is easier and before we end up creating a lot of new
> fixed
> >>
> >> point code.
> >>
> >> My plate is full right now, but hopefully I can interest someone
> else
> >> in
> >> doing a cleanup cycle?  (Donning my Tom Sawyer hat... ;-)
> >>
> >> 			...jim