1GD::Polyline(3) User Contributed Perl Documentation GD::Polyline(3)
2
6 GD::Polyline - Polyline object and Polygon utilities (including
7 splines) for use with GD
8
10 use GD;
11 use GD::Polyline;
12 # create an image
14 $image = GD::Image->new (500,300);
15 $white = $image->colorAllocate(255,255,255);
16 $black = $image->colorAllocate( 0, 0, 0);
17 $red = $image->colorAllocate(255, 0, 0);
18 # create a new polyline
20 $polyline = GD::Polyline->new;
21 # add some points
23 $polyline->addPt( 0, 0);
24 $polyline->addPt( 0,100);
25 $polyline->addPt( 50,125);
26 $polyline->addPt(100, 0);
27 # polylines can use polygon methods (and vice versa)
29 $polyline->offset(200,100);
30 # rotate 60 degrees, about the centroid
32 $polyline->rotate(3.14159/3, $polyline->centroid());
33 # scale about the centroid
35 $polyline->scale(1.5, 2, $polyline->centroid());
36 # draw the polyline
38 $image->polydraw($polyline,$black);
39 # create a spline, which is also a polyine
41 $spline = $polyline->addControlPoints->toSpline;
42 $image->polydraw($spline,$red);
43 # output the png
45 binmode STDOUT;
46 print $image->png;
47
49 Polyline.pm extends the GD module by allowing you to create polylines.
50 Think of a polyline as "an open polygon", that is, the last vertex is
51 not connected to the first vertex (unless you expressly add the same
52 value as both points).
53 For the remainder of this doc, "polyline" will refer to a GD::Polyline,
55 "polygon" will refer to a GD::Polygon that is not a polyline, and
56 "polything" and "$poly" may be either.
57 The big feature added to GD by this module is the means to create
59 splines, which are approximations to curves.
60
62 GD::Polyline defines the following class:
63 "GD::Polyline"
65 A polyline object, used for storing lists of vertices prior to
66 rendering a polyline into an image.
67 "new"
69 "GD::Polyline->new" class method
70 Create an empty polyline with no vertices.
72 $polyline = GD::Polyline->new;
74 $polyline->addPt( 0, 0);
76 $polyline->addPt( 0,100);
77 $polyline->addPt( 50,100);
78 $polyline->addPt(100, 0);
79 $image->polydraw($polyline,$black);
81 In fact GD::Polyline is a subclass of GD::Polygon, so all polygon
83 methods (such as offset and transform) may be used on polylines.
84 Some new methods have thus been added to GD::Polygon (such as
85 rotate) and a few updated/modified/enhanced (such as scale) in
86 this module. See section "New or Updated GD::Polygon Methods" for
87 more info.
88 Note that this module is very "young" and should be considered subject
90 to change in future releases, and/or possibly folded in to the existing
91 polygon object and/or GD module.
92
94 The following methods (defined in GD.pm) are OVERRIDDEN if you use this
95 module.
96 All effort has been made to provide 100% backward compatibility, but if
98 you can confirm that has not been achieved, please consider that a bug
99 and let the the author of Polyline.pm know.
100 "scale"
102 "$poly->scale($sx, $sy, $cx, $cy)" object method -- UPDATE to
103 GD::Polygon::scale
104 Scale a polything in along x-axis by $sx and along the y-axis by
106 $sy, about centery point ($cx, $cy).
107 Center point ($cx, $cy) is optional -- if these are omitted, the
109 function will scale about the origin.
110 To flip a polything, use a scale factor of -1. For example, to
112 flip the polything top to bottom about line y = 100, use:
113 $poly->scale(1, -1, 0, 100);
115
117 The following methods are added to GD::Polygon, and thus can be used by
118 polygons and polylines.
119 Don't forget: a polyline is a GD::Polygon, so GD::Polygon methods like
121 offset() can be used, and they can be used in GD::Image methods like
122 filledPolygon().
123 "rotate"
125 "$poly->rotate($angle, $cx, $cy)" object method
126 Rotate a polything through $angle (clockwise, in radians) about
128 center point ($cx, $cy).
129 Center point ($cx, $cy) is optional -- if these are omitted, the
131 function will rotate about the origin
132 In this function and other angle-oriented functions in
134 GD::Polyline, positive $angle corresponds to clockwise rotation.
135 This is opposite of the usual Cartesian sense, but that is because
136 the raster is opposite of the usual Cartesian sense in that the
137 y-axis goes "down".
138 "centroid"
140 "($cx, $cy) = $poly->centroid($scale)" object method
141 Calculate and return ($cx, $cy), the centroid of the vertices of
143 the polything. For example, to rotate something 180 degrees about
144 it's centroid:
145 $poly->rotate(3.14159, $poly->centroid());
147 $scale is optional; if supplied, $cx and $cy are multiplied by
149 $scale before returning. The main use of this is to shift an
150 polything to the origin like this:
151 $poly->offset($poly->centroid(-1));
153 "segLength"
155 "@segLengths = $poly->segLength()" object method
156 In array context, returns an array the lengths of the segments in
158 the polything. Segment n is the segment from vertex n to vertex
159 n+1. Polygons have as many segments as vertices; polylines have
160 one fewer.
161 In a scalar context, returns the sum of the array that would have
163 been returned in the array context.
164 "segAngle"
166 "@segAngles = $poly->segAngle()" object method
167 Returns an array the angles of each segment from the x-axis.
169 Segment n is the segment from vertex n to vertex n+1. Polygons
170 have as many segments as vertices; polylines have one fewer.
171 Returned angles will be on the interval 0 <= $angle < 2 * pi and
173 angles increase in a clockwise direction.
174 "vertexAngle"
176 "@vertexAngles = $poly->vertexAngle()" object method
177 Returns an array of the angles between the segment into and out of
179 each vertex. For polylines, the vertex angle at vertex 0 and the
180 last vertex are not defined; however $vertexAngle[0] will be undef
181 so that $vertexAngle[1] will correspond to vertex 1.
182 Returned angles will be on the interval 0 <= $angle < 2 * pi and
184 angles increase in a clockwise direction.
185 Note that this calculation does not attempt to figure out the
187 "interior" angle with respect to "inside" or "outside" the
188 polygon, but rather, just the angle between the adjacent segments
189 in a clockwise sense. Thus a polygon with all right angles will
190 have vertex angles of either pi/2 or 3*pi/2, depending on the way
191 the polygon was "wound".
192 "toSpline"
194 "$poly->toSpline()" object method & factory method
195 Create a new polything which is a reasonably smooth curve using
197 cubic spline algorithms, often referred to as Bezier curves. The
198 "source" polything is called the "control polything". If it is a
199 polyline, the control polyline must have 4, 7, 10, or some number
200 of vertices of equal to 3n+1. If it is a polygon, the control
201 polygon must have 3, 6, 9, or some number of vertices of equal to
202 3n.
203 $spline = $poly->toSpline();
205 $image->polydraw($spline,$red);
206 In brief, groups of four points from the control polyline are
208 considered "control points" for a given portion of the spline: the
209 first and fourth are "anchor points", and the spline passes
210 through them; the second and third are "director points". The
211 spline does not pass through director points, however the spline
212 is tangent to the line segment from anchor point to adjacent
213 director point.
214 The next portion of the spline reuses the previous portion's last
216 anchor point. The spline will have a cusp (non-continuous slope)
217 at an anchor point, unless the anchor points and its adjacent
218 director point are colinear.
219 In the current implementation, toSpline() return a fixed number of
221 segments in the returned polyline per set-of-four control points.
222 In the future, this and other parameters of the algorithm may be
223 configurable.
224 "addControlPoints"
226 "$polyline->addControlPoints()" object method & factory method
227 So you say: "OK. Splines sound cool. But how can I get my anchor
229 points and its adjacent director point to be colinear so that I
230 have a nice smooth curves from my polyline?" Relax! For The
231 Lazy: addControlPoints() to the rescue.
232 addControlPoints() returns a polyline that can serve as the
234 control polyline for toSpline(), which returns another polyline
235 which is the spline. Is your head spinning yet? Think of it this
236 way:
237 + If you have a polyline, and you have already put your control
239 points where you want them, call toSpline() directly.
240 Remember, only every third vertex will be "on" the spline.
241 You get something that looks like the spline "inscribed"
243 inside the control polyline.
244 + If you have a polyline, and you want all of its vertices on
246 the resulting spline, call addControlPoints() and then
247 toSpline():
248 $control = $polyline->addControlPoints();
250 $spline = $control->toSpline();
251 $image->polyline($spline,$red);
252 You get something that looks like the control polyline
254 "inscribed" inside the spline.
255 Adding "good" control points is subjective; this particular
257 algorithm reveals its author's tastes. In the future, you may be
258 able to alter the taste slightly via parameters to the algorithm.
259 For The Hubristic: please build a better one!
260 And for The Impatient: note that addControlPoints() returns a
262 polyline, so you can pile up the call like this, if you'd like:
263 $image->polyline($polyline->addControlPoints()->toSpline(),$mauve);
265
267 "polyline"
268 "$image->polyline(polyline,color)" object method
269 $image->polyline($polyline,$black)
271 This draws a polyline with the specified color. Both real color
273 indexes and the special colors gdBrushed, gdStyled and
274 gdStyledBrushed can be specified.
275 Neither the polyline() method or the polygon() method are very
277 picky: you can call either method with either a GD::Polygon or a
278 GD::Polyline. The method determines if the shape is "closed" or
279 "open" as drawn, not the object type.
280 "polydraw"
282 "$image->polydraw(polything,color)" object method
283 $image->polydraw($poly,$black)
285 This method draws the polything as expected (polygons are closed,
287 polylines are open) by simply checking the object type and calling
288 either $image->polygon() or $image->polyline().
289
291 Please see file "polyline-examples.pl" that is included with the
292 distribution.
293
295 For more info on Bezier splines, see
296 http://www.webreference.com/dlab/9902/bezier.html.
297
299 On the drawing board are additional features such as:
300 - polygon winding algorithms (to determine if a point is "inside" or "outside" the polygon)
302 - new polygon from bounding box
304 - find bounding polygon (tightest fitting simple convex polygon for a given set of vertices)
306 - addPts() method to add many points at once
308 - clone() method for polygon
310 - functions to interwork GD with SVG
312 Please provide input on other possible features you'd like to see.
314
316 This module has been written by Daniel J. Harasty. Please send
317 questions, comments, complaints, and kudos to him at harasty@cpan.org.
318 Thanks to Lincoln Stein for input and patience with me and this, my
320 first CPAN contribution.
321
323 The Polyline.pm module is copyright 2002, Daniel J. Harasty. It is
324 distributed under the same terms as Perl itself. See the "Artistic
325 License" in the Perl source code distribution for licensing terms.
326 The latest version of Polyline.pm is available at your favorite CPAN
328 repository and/or along with GD.pm by Lincoln D. Stein at
329 http://stein.cshl.org/WWW/software/GD.
330perl v5.36.0 2022-07-22 GD::Polyline(3)