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

Jim Graham james.graham at oracle.com
Wed Oct 20 10:20:18 PDT 2010

```On 10/20/10 7:54 AM, Denis Lila wrote:
>> In #2, you have a bunch of "I'() || B'()" which I read as "the slope
>> of the derivative (i.e. acceleration) is equal", don't you really mean
>> "I() || B()" which would mean the original curves should be parallel?
>> Otherwise you could say "I'() == B'()", but I think you want to show
>> parallels because that shows how you can use the dxy1,dxy4 values as
>> the parallel equivalents.
>
> Not really. I've updated the comment explaining what || does, and
> it should be clearer now. Basically, A(t) || B(t) means that vectors
> A(t) and B(t) are parallel (i.e. A(t) = c*B(t), for some nonzero t),
> not that curves A and B are parallel at t.

I'm not sure we are on the same page here.

I'() is usually the symbol indicating the "derivative" of I().  My issue
is not with the || operator, but with the fact that you are applying it
to the I'() instead of I().

Also, how is A(t) and B(t) are parallel not the same as "the curves A
and B are parallel at t"?

Also, A(t) = c*B(t) is always true for all A and B and all t if you take
a sample in isolation.  Parallel means something like "A(t) = c*B(t)
with the same value of c for some interval around t", not that the
values at t can be expressed as a multiple.

Again, I'() || B'() says to me that the derivative curves are parallel,
not that the original curves are parallel...

...jim

```