phpman > perldoc > GD::Polyline

NAME
    GD::Polyline - Polyline object and Polygon utilities (including splines) for use with GD

SYNOPSIS
            use GD;
            use GD::Polyline;

            # create an image
            $image = GD::Image->new (500,300);
            $white  = $image->colorAllocate(255,255,255);
            $black  = $image->colorAllocate(  0,  0,  0);
            $red    = $image->colorAllocate(255,  0,  0);

            # create a new polyline
            $polyline = GD::Polyline->new;

            # add some points
            $polyline->addPt(  0,  0);
            $polyline->addPt(  0,100);
            $polyline->addPt( 50,125);
            $polyline->addPt(100,  0);

            # polylines can use polygon methods (and vice versa)
            $polyline->offset(200,100);

            # rotate 60 degrees, about the centroid
            $polyline->rotate(3.14159/3, $polyline->centroid());

            # scale about the centroid
            $polyline->scale(1.5, 2, $polyline->centroid());

            # draw the polyline
            $image->polydraw($polyline,$black);

            # create a spline, which is also a polyine
            $spline = $polyline->addControlPoints->toSpline;
            $image->polydraw($spline,$red);

            # output the png
            binmode STDOUT;
            print $image->png;

DESCRIPTION
    Polyline.pm extends the GD module by allowing you to create polylines. Think of a polyline as
    "an open polygon", that is, the last vertex is not connected to the first vertex (unless you
    expressly add the same value as both points).

    For the remainder of this doc, "polyline" will refer to a GD::Polyline, "polygon" will refer to
    a GD::Polygon that is not a polyline, and "polything" and "$poly" may be either.

    The big feature added to GD by this module is the means to create splines, which are
    approximations to curves.

The Polyline Object
    GD::Polyline defines the following class:

    "GD::Polyline"
         A polyline object, used for storing lists of vertices prior to rendering a polyline into an
         image.

    "new"
         "GD::Polyline->new" *class method*

         Create an empty polyline with no vertices.

                 $polyline = GD::Polyline->new;

                 $polyline->addPt(  0,  0);
                 $polyline->addPt(  0,100);
                 $polyline->addPt( 50,100);
                 $polyline->addPt(100,  0);

                 $image->polydraw($polyline,$black);

         In fact GD::Polyline is a subclass of GD::Polygon, so all polygon methods (such as offset
         and transform) may be used on polylines. Some new methods have thus been added to
         GD::Polygon (such as rotate) and a few updated/modified/enhanced (such as scale) *in this
         module*. See section "New or Updated GD::Polygon Methods" for more info.

    Note that this module is very "young" and should be considered subject to change in future
    releases, and/or possibly folded in to the existing polygon object and/or GD module.

Updated Polygon Methods
    The following methods (defined in GD.pm) are OVERRIDDEN if you use this module.

    All effort has been made to provide 100% backward compatibility, but if you can confirm that has
    not been achieved, please consider that a bug and let the the author of Polyline.pm know.

    "scale"
         "$poly->scale($sx, $sy, $cx, $cy)" *object method -- UPDATE to GD::Polygon::scale*

         Scale a polything in along x-axis by $sx and along the y-axis by $sy, about centery point
         ($cx, $cy).

         Center point ($cx, $cy) is optional -- if these are omitted, the function will scale about
         the origin.

         To flip a polything, use a scale factor of -1. For example, to flip the polything top to
         bottom about line y = 100, use:

                 $poly->scale(1, -1, 0, 100);

New Polygon Methods
    The following methods are added to GD::Polygon, and thus can be used by polygons and polylines.

    Don't forget: a polyline is a GD::Polygon, so GD::Polygon methods like offset() can be used, and
    they can be used in GD::Image methods like filledPolygon().

    "rotate"
         "$poly->rotate($angle, $cx, $cy)" *object method*

         Rotate a polything through $angle (clockwise, in radians) about center point ($cx, $cy).

         Center point ($cx, $cy) is optional -- if these are omitted, the function will rotate about
         the origin

         In this function and other angle-oriented functions in GD::Polyline, positive $angle
         corresponds to clockwise rotation. This is opposite of the usual Cartesian sense, but that
         is because the raster is opposite of the usual Cartesian sense in that the y-axis goes
         "down".

    "centroid"
         "($cx, $cy) = $poly->centroid($scale)" *object method*

         Calculate and return ($cx, $cy), the centroid of the vertices of the polything. For
         example, to rotate something 180 degrees about it's centroid:

                 $poly->rotate(3.14159, $poly->centroid());

         $scale is optional; if supplied, $cx and $cy are multiplied by $scale before returning. The
         main use of this is to shift an polything to the origin like this:

                 $poly->offset($poly->centroid(-1));

    "segLength"
         "@segLengths = $poly->segLength()" *object method*

         In array context, returns an array the lengths of the segments in the polything. Segment n
         is the segment from vertex n to vertex n+1. Polygons have as many segments as vertices;
         polylines have one fewer.

         In a scalar context, returns the sum of the array that would have been returned in the
         array context.

    "segAngle"
         "@segAngles = $poly->segAngle()" *object method*

         Returns an array the angles of each segment from the x-axis. Segment n is the segment from
         vertex n to vertex n+1. Polygons have as many segments as vertices; polylines have one
         fewer.

         Returned angles will be on the interval 0 <= $angle < 2 * pi and angles increase in a
         clockwise direction.

    "vertexAngle"
         "@vertexAngles = $poly->vertexAngle()" *object method*

         Returns an array of the angles between the segment into and out of each vertex. For
         polylines, the vertex angle at vertex 0 and the last vertex are not defined; however
         $vertexAngle[0] will be undef so that $vertexAngle[1] will correspond to vertex 1.

         Returned angles will be on the interval 0 <= $angle < 2 * pi and angles increase in a
         clockwise direction.

         Note that this calculation does not attempt to figure out the "interior" angle with respect
         to "inside" or "outside" the polygon, but rather, just the angle between the adjacent
         segments in a clockwise sense. Thus a polygon with all right angles will have vertex angles
         of either pi/2 or 3*pi/2, depending on the way the polygon was "wound".

    "toSpline"
         "$poly->toSpline()" *object method & factory method*

         Create a new polything which is a reasonably smooth curve using cubic spline algorithms,
         often referred to as Bezier curves. The "source" polything is called the "control
         polything". If it is a polyline, the control polyline must have 4, 7, 10, or some number of
         vertices of equal to 3n+1. If it is a polygon, the control polygon must have 3, 6, 9, or
         some number of vertices of equal to 3n.

                 $spline = $poly->toSpline();
                 $image->polydraw($spline,$red);

         In brief, groups of four points from the control polyline are considered "control points"
         for a given portion of the spline: the first and fourth are "anchor points", and the spline
         passes through them; the second and third are "director points". The spline does not pass
         through director points, however the spline is tangent to the line segment from anchor
         point to adjacent director point.

         The next portion of the spline reuses the previous portion's last anchor point. The spline
         will have a cusp (non-continuous slope) at an anchor point, unless the anchor points and
         its adjacent director point are colinear.

         In the current implementation, toSpline() return a fixed number of segments in the returned
         polyline per set-of-four control points. In the future, this and other parameters of the
         algorithm may be configurable.

    "addControlPoints"
         "$polyline->addControlPoints()" *object method & factory method*

         So you say: "OK. Splines sound cool. But how can I get my anchor points and its adjacent
         director point to be colinear so that I have a nice smooth curves from my polyline?" Relax!
         For The Lazy: addControlPoints() to the rescue.

         addControlPoints() returns a polyline that can serve as the control polyline for
         toSpline(), which returns another polyline which is the spline. Is your head spinning yet?
         Think of it this way:

         +    If you have a polyline, and you have already put your control points where you want
              them, call toSpline() directly. Remember, only every third vertex will be "on" the
              spline.

              You get something that looks like the spline "inscribed" inside the control polyline.

         +    If you have a polyline, and you want all of its vertices on the resulting spline, call
              addControlPoints() and then toSpline():

                      $control = $polyline->addControlPoints();
                      $spline  = $control->toSpline();
                      $image->polyline($spline,$red);

              You get something that looks like the control polyline "inscribed" inside the spline.

         Adding "good" control points is subjective; this particular algorithm reveals its author's
         tastes. In the future, you may be able to alter the taste slightly via parameters to the
         algorithm. For The Hubristic: please build a better one!

         And for The Impatient: note that addControlPoints() returns a polyline, so you can pile up
         the call like this, if you'd like:

                 $image->polyline($polyline->addControlPoints()->toSpline(),$mauve);

New GD::Image Methods
    "polyline"
         "$image->polyline(polyline,color)" *object method*

                 $image->polyline($polyline,$black)

         This draws a polyline with the specified color. Both real color indexes and the special
         colors gdBrushed, gdStyled and gdStyledBrushed can be specified.

         Neither the polyline() method or the polygon() method are very picky: you can call either
         method with either a GD::Polygon or a GD::Polyline. The *method* determines if the shape is
         "closed" or "open" as drawn, *not* the object type.

    "polydraw"
         "$image->polydraw(polything,color)" *object method*

                 $image->polydraw($poly,$black)

         This method draws the polything as expected (polygons are closed, polylines are open) by
         simply checking the object type and calling either $image->polygon() or $image->polyline().

Examples
    Please see file "polyline-examples.pl" that is included with the distribution.

See Also
    For more info on Bezier splines, see http://www.webreference.com/dlab/9902/bezier.html.

Future Features
    On the drawing board are additional features such as:

            - polygon winding algorithms (to determine if a point is "inside" or "outside" the polygon)

            - new polygon from bounding box

            - find bounding polygon (tightest fitting simple convex polygon for a given set of vertices)

            - addPts() method to add many points at once

            - clone() method for polygon

            - functions to interwork GD with SVG

    Please provide input on other possible features you'd like to see.

Author
    This module has been written by Daniel J. Harasty. Please send questions, comments, complaints,
    and kudos to him at harasty AT cpan.org.

    Thanks to Lincoln Stein for input and patience with me and this, my first CPAN contribution.

Copyright Information
    The Polyline.pm module is copyright 2002, Daniel J. Harasty. It is distributed under the same
    terms as Perl itself. See the "Artistic License" in the Perl source code distribution for
    licensing terms.

    The latest version of Polyline.pm is available at your favorite CPAN repository and/or along
    with GD.pm by Lincoln D. Stein at http://stein.cshl.org/WWW/software/GD.