Thursday, November 12, 2009

Vector and SVG: Almost There

I noticed from #perl6 that chromatic fixed a memory leak in Parrot recently, and that fix made its way to Rakudo today. I thought, hey, I've been having a bus error. Could that be caused by an out-of-memory condition? So I upgraded Rakudo, and haven't seen the bus error since. (The "too many positional arguments: 3 passed, 1 expected" remain if I crank up the number of samples taken of each curve, but hopefully now I'll be able to track that down without being knocked around by bus errors.)

So, the first thing I did to get SVG working with Nubs and Polynomial was to write a simple class which converts from "normal" XY space to SVG coordinates (which I'm referring to as NM coordinates in this code).
class Vector { ... }
subset Vector2 of Vector where { $^v.Dim == 2 };

class SVGPad
has Vector2 $.xy_min;
has Vector2 $.xy_max;
has Vector2 $.mn_min;
has Vector2 $.mn_max;

multi method new(Vector2 $xy_min, Vector2 $xy_max, Vector2 $mn_min, Vector2 $mn_max)
self.bless(*, xy_min => $xy_min, xy_max => $xy_max, mn_min => $mn_min, mn_max => $mn_max);

multi method xy2mn(Vector2 $xy)
my $t = ($xy - $.xy_min).coordinates >>/<< ($.xy_max - $.xy_min).coordinates;
return $.mn_min +$.mn_max - $.mn_min).coordinates >>*<< $t);

So the code to use this (for now) is just
class SVGPad { ... }
class Nubs { ... }
class Polynomial { ... }
sub MakePath($curve, Range $range, SVGPad $pad)
my @points = RangeOfSize($range.from, $, 10).map({$pad.xy2mn($curve.evaluate($_))});
my $start = @points.shift;
my $path = "M {$start.coordinates[0]} {$start.coordinates[1]}";
for @points -> $v
$path ~= " L {$v.coordinates[0]} {$v.coordinates[1]}";
return $path;

my @control_points = (, -2),, 0),, 1),, 1),, 2),, 2),, 2));
my @knots = (-1, -1, -1, -1, 1, 2, 2, 3, 3, 3, 3);
my Nubs $nubs =,, @control_points);
my Polynomial $poly1 = $nubs.evaluate(0,, 1.0));
my Polynomial $poly2 = $nubs.evaluate(1.5,, 1.0));
my Polynomial $poly3 = $nubs.evaluate(2.5,, 1.0));

my $pad =, -2.5),, 2.5),, 0),, 400));
my $svg = svg => [
:width(400), :height(400),
path => [
:d(MakePath($nubs, -1..3, $pad)), :stroke("blue"), :stroke-width(2), :fill("none")
path => [
:d(MakePath($poly1, -2..2, $pad)), :stroke("green"), :stroke-width(1), :fill("none")
path => [
:d(MakePath($poly2, 0..3, $pad)), :stroke("red"), :stroke-width(1), :fill("none")
path => [
:d(MakePath($poly3, 1..4, $pad)), :stroke("white"), :stroke-width(1), :fill("none")

say SVG.serialize($svg);

MakePath is a simple function which takes a "curve" (that is, an object which has an evaluate function which goes from t to x, y), a Perl 6 Range to evaluate it over, and an SVGPad, and returns a SVG path object. Then we set up a fairly simple NUBS curve, use the Nubs to Polynomial version of the evaluate function to generate the corresponding Polynomial for each segment of the curve, and output all four curves to SVG. This is still a crude first approximation, but it does work; if I knew how to include SVG in this post I could show it. Next time, hopefully.

1 comment:

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