Splitting a rendered path at a specified point using Batik

[Web Query <we...@shermantech.com>]

Hi,

I was wondering if there was a way for Batik to take a rather complex 
path and split it into two paths at a specified point.  Here is the 
situation:

I have a very complex path composed of many curves and lines that needs 
to be split up into segments at specified points.  So I have created a 
Batik-based program that allows me to select a path and return to me the 
point at which I selected the path.  At this selected point I would like 
to split the path into two path segments.

Can Batik do this?  If not, is there a good algorithm for doing this?

Thanks,
Chris

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Re: Splitting a rendered path at a specified point using Batik

[Thomas DeWeese <Th...@Kodak.com>]

Hi Chris,

Web Query wrote:

> I was wondering if there was a way for Batik to take a rather complex 
> path and split it into two paths at a specified point.  Here is the 
> situation:

    The short answer is no.  The longer answer is possibly shortly.
As part of implementing the new flowText element (which supports
flow into arbitrary regions).  I have developed a sort of 'geometry
library'.  This does not do exactly what you are looking for but
would be a big help.

> I have a very complex path composed of many curves and lines that needs 
> to be split up into segments at specified points.  So I have created a 
> Batik-based program that allows me to select a path and return to me the 
> point at which I selected the path.  At this selected point I would like 
> to split the path into two path segments.
> 
> Can Batik do this?  If not, is there a good algorithm for doing this?

    Basically you need to learn how to subdivide a cubic bezier at
a particular 'time':

     /**
      * Subdivides this Cubic curve into two curves at given t.
      * @param c0 if non-null contains portion of curve from 0->t.
      * @param c1 if non-null contains portion of curve from t->1.
      */
     public void subdivide(double t, Cubic c0, Cubic c1) {
         if ((c0 == null) && (c1 == null)) return;

         Point2D.Double np = eval(t);
         Point2D.Double npd = evalDt(t);

         if (c0 != null) {
             c0.p1.x = p1.x;
             c0.p1.y = p1.y;
             c0.p2.x = (p2.x+p1.x)*t;
             c0.p2.y = (p2.y+p1.y)*t;

             c0.p3.x = np.x-(npd.x*t/3);
             c0.p3.y = np.y-(npd.y*t/3);
             c0.p4.x = np.x;
             c0.p4.y = np.y;
         }

         if (c1 != null) {
             c1.p1.x = np.x;
             c1.p1.y = np.y;
             c1.p2.x = np.x+(npd.x*(1-t)/3);
             c1.p2.y = np.y+(npd.y*(1-t)/3);

             c1.p3.x = (p4.x+p3.x)*(1-t);
             c1.p3.y = (p4.y+p3.y)*(1-t);
             c1.p4.x = p4.x;
             c1.p4.y = p4.y;
         }
     }

     public Point2D.Double evalDt(double t) {
         double x = 3*(  (p2.x-p1.x)*(1-t)*(1-t) +
                       2*(p3.x-p2.x)*(1-t)*t +
                         (p4.x-p3.x)*t*t);
         double y = 3*(  (p2.y-p1.y)*(1-t)*(1-t) +
                       2*(p3.y-p2.y)*(1-t)*t +
                         (p4.y-p3.y)*t*t);
         return new Point2D.Double(x, y);
     }


     public Point2D.Double eval(double t) {
         double x = ((1-t)*(1-t)*(1-t)*p1.x +
                     3*(t* (1-t)*(1-t)*p2.x +
                        t* t*    (1-t)*p3.x) +
                     t*t*t            *p4.x);
         double y = ((1-t)*(1-t)*(1-t)*p1.y +
                     3*(t* (1-t)*(1-t)*p2.y +
                        t* t*    (1-t)*p3.y) +
                     t*t*t            *p4.y);
         return new Point2D.Double(x, y);
     }



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