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

[Jim Graham]

Round 4...

On 10/6/2010 1:36 PM, Denis Lila wrote:
>
> webrev:
> http://icedtea.classpath.org/~dlila/webrevs/noflatten/webrev/

BezCurve.java:

I'd add some "set()" methods to BezCurve/Curve and then use a scratch 
instance in Renderer (and other places?) to reuse those calculations, 
such as:

Curve constructors (obviously)
Renderer.curveOrQuadTo()
Renderer.initQuad()
Renderer.initCurve()
Stroker.findSubdivPoints()

lines 179,182 - using your d* variables, wouldn't these be:
    a = 2*(dax*dax + day*day)
    b = 3*(dax*dbx + day*dby)
    c = 2*(dax*cx + day*cy) + dbx*dbx + dby*dby
    d = dbx*cx + dby*cy
It has fewer multiplies and more of the multipliers are powers of 2 
which are faster than non-power-of-2 multiplies.

line 206,210 - a nit - it didn't really confuse me, but halfway through 
reading this it occurs to me that these are really t0 and t1, right?

line 212 - if x0 (t0?) is 0 then you don't need to include it in the 
roots, no?

line 249,257 - these corrections are exponential compared to the sample 
code on the wikipedia page - was that the "slight modification" that you 
mentioned in the comments?

line 303 - isn't it enough to just look at the previous T value (or keep 
a running "prevt" variable) rather than update every T value in the 
array?  Isn't this enough?
     int prevt = 0; /* field in Iterator */
     next() {
         curt = Ts[next];
         split = (curt - prevt) / (1 - prevt);
         prevt = curt;
     }

ROCsq - I looked at the wikipedia article and it wasn't clear how it 
directly related to your function since the article is dealing with the 
curvature of a function graphed against its own t, but you are dealing 
with 2 parametric equations combined and graphed against each other.  I 
think I'm going to have to just trust you on this one for now.  :-(

Done with BezCurve.java...

Stroker.java:

lines 558 (et al) - create a helper function for all of these 
(degenerates to a line) cases?

lines 621-626 and 643-646 - I'm not sure what the derivation of these 
lines are.  I tried to do my own equations, but I seem to be heading in 
a different direction than you used and it didn't seem like I was going 
to converge.  What equations did you set up to solve to get these 
calculations?  From what I can see we have:
   - new p1,p4 are calculated
   - new p(0.5) is calculated
   - the corresponding dx,dy at t=0,0.5,1 (gives slopes)
   - slopes at t=0, 0.5 and 1 should be the same for all curves
and what you are trying to compute are two scaling constants c1 and c2 
that represent how much to scale the dx1,dy1 and dx4,dy4 values to get a 
curve that interpolates both position and slope at t=0.5.  A comment 
might help here...  :-(

line 687 - dup?

line 856 - use a scratch Curve instance and set methods to reduce GC?

line 857 - this is true if the first vector is parallel to either axis, 
but the comment after it says only "parallel to the x axis" - is that a 
problem?  Also, if both are 0 then no parallel constraint is applied 
even if it does start out parallel.  I imagine that this is all OK 
because the "both 0" case should be rare/non-existant and the y-axis 
case will also benefit from the same optimization...?

lines 861-863:  sin/cos and atan2 cancel each other out.  It is faster 
to compute the hypotenuse and then divide the x and y by the hypotenuse 
to get the cos and sin.  (cos = x/hypot; sin = y/hypot;)

Cache and TileGenerator look ok...

I think I'm done at this point except for not understanding the 
"parallel cubic" equations I mentioned above and the ROCsq method...

			...jim