Triangle2

Triangles in 2D space

PhilipRBrenan@yahoo.com, 2004, Perl License

Synopsis

Example t/triangle2.t

 #_ Triangle ___________________________________________________________
 # Test 2d triangles    
 # philiprbrenan@yahoo.com, 2004, Perl License    
 #______________________________________________________________________
 
 use Math::Zap::Triangle2;
 use Math::Zap::Vector2;
 use Test::Simple tests=>27;
  
 $a = triangle2
  (vector2(0, 0), 
   vector2(2, 0), 
   vector2(0, 2),
  );
  
 $b = triangle2
  (vector2( 0,  0), 
   vector2( 4,  0), 
   vector2( 0,  4),
  );
  
 $c = triangle2
  (vector2( 0,  0), 
   vector2(-4,  0), 
   vector2( 0, -4),
  );
  
 $d = $b - vector2(1,1);
 $e = $c + vector2(1,1);
 
 #print "a=$a\nb=$b\nc=$c\nd=$d\ne=$e\n";
 
 ok($a->containsPoint(vector2( 1,  1)));
 ok($a->containsPoint(vector2( 1,  1)));
 ok($b->containsPoint(vector2( 2,  0)));
 ok($b->containsPoint(vector2( 1,  0)));
 ok($c->containsPoint(vector2(-1,  0)));
 ok($c->containsPoint(vector2(-2,  0)));
 ok($d->containsPoint(vector2( 1, -1)));
 
 ok(!$a->containsPoint(vector2( 9,  1)));
 ok(!$a->containsPoint(vector2( 1,  9)));
 ok(!$b->containsPoint(vector2( 2,  9)));
 ok(!$b->containsPoint(vector2( 9,  0)));
 ok(!$c->containsPoint(vector2(-9,  0)));
 ok(!$c->containsPoint(vector2(-2,  9)));
 ok(!$d->containsPoint(vector2( 9, -1)));
 
 ok( $a->containsPoint(vector2(0.5, 0.5)));
 ok(!$a->containsPoint(vector2( -1,  -1)));
 
 ok(vector2(1,2)->rightAngle == vector2(-2, 1));
 ok(vector2(1,0)->rightAngle == vector2( 0, 1));
 
 ok($a->area == 2);
 ok($c->area == 8);
 
 eval { triangle2(vector2(0, 0), vector2(3, -6), vector2(-3, 6))};
 ok($@ =~ /^Narrow triangle2/, 'Narrow triangle');
 
 $t = triangle2(vector2(0,0),vector2(0,10),vector2( 10,0));
 $T = triangle2(vector2(0,0),vector2(0,10),vector2(-10,10))+vector2(5, -2);
 @p = $t->ring($T);
 #print "$_\n" for(@p);
 ok($p[0] == vector2(0, 8), 'Ring 0');
 ok($p[1] == vector2(2, 8), 'Ring 1');
 ok($p[2] == vector2(5, 5), 'Ring 2');
 ok($p[3] == vector2(5, 0), 'Ring 3');
 ok($p[4] == vector2(3, 0), 'Ring 4');
 ok($p[5] == vector2(0, 3), 'Ring 5');

Description

Triangles in 2d space

 package Math::Zap::Triangle2;
 $VERSION=1.07;
 use Math::Zap::Line2;
 use Math::Zap::Matrix2 new2v=>'matrix2New2v';
 use Math::Zap::Vector2 check=>'vector2Check';
 use Math::Zap::Vector  check=>'vectorCheck';
 use Math::Trig;            
 use Carp qw(cluck confess);
 use constant debug => 0; # Debugging level
 
 

Constructors

new

Create a triangle from 3 vectors specifying the coordinates of each corner in space coordinates.

 sub new($$$)
  {vector2Check(@_) if debug;
   my $t = bless {a=>$_[0], b=>$_[1], c=>$_[2]};
   narrow($t, 1);      
   $t;
  }
 
 

triangle2

Create a triangle from 3 vectors specifying the coordinates of each corner in space coordinates - synonym for "new".

 sub triangle2($$$) {new($_[0],$_[1],$_[2])};
 
 

newnnc

New without narrowness check

 sub newnnc($$$)
  {vector2Check(@_) if debug;
   bless {a=>$_[0], b=>$_[1], c=>$_[2]};
  }
 
 

newV

Create a triangle from the x,y components of 3 3d vectors.

 sub newV($$$)
  {vectorCheck(@_) if debug;
   my $t = bless
    {a=>vector2($_[0]->{x}, $_[0]->{y}),
     b=>vector2($_[1]->{x}, $_[1]->{y}),
     c=>vector2($_[2]->{x}, $_[2]->{y})};
   narrow($t, 1);      
   $t;
  }
 
 

newVnnc

Create a triangle from the x,y components of 3 3d vectors without narrowness checking - assumes caller will do thir own.

 sub newVnnc($$$)
  {vectorCheck(@_) if debug;
   bless
    {a=>vector2($_[0]->{x}, $_[0]->{y}),
     b=>vector2($_[1]->{x}, $_[1]->{y}),
     c=>vector2($_[2]->{x}, $_[2]->{y})};
  }
 
 

Methods

accuracy

Get/Set accuracy for comparisons

 my $accuracy = 1e-10;
 
 sub accuracy
  {return $accuracy unless scalar(@_);
   $accuracy = shift();
  }
 
 

narrow

Narrow (colinear) colinear?

 sub narrow($$)
  {my $t = shift;  # Triangle
   my $a = 1e-2;   # Accuracy
   my $A = shift;  # Action 0: return indicator, 1: confess 
   my $b = vector($t->{b}{x}-$t->{a}{x}, $t->{b}{y}-$t->{a}{y}, 0);                                           
   my $c = vector($t->{c}{x}-$t->{a}{x}, $t->{c}{y}-$t->{a}{y}, 0);                                           
   my $n = ($b x $c)->length < $a;
   confess "Narrow triangle2" if $n and $A;
   $n;      
  }
 
 

check

Check its a triangle

 sub check(@)
  {if (debug)
    {for my $t(@_)
      {confess "$t is not a triangle2" unless ref($t) eq __PACKAGE__;
      }
    }
   @_;
  }
 
 

is

Test its a triangle

 sub is(@)
  {for my $t(@_)
    {return 0 unless ref($t) eq __PACKAGE__;
    }
   'triangle2';
  }
 
 

components

Components of a triangle

 sub a($)   {check(@_) if debug; $_[0]->{a}}
 sub b($)   {check(@_) if debug; $_[0]->{b}}
 sub c($)   {check(@_) if debug; $_[0]->{c}}
 
 sub ab($)  {check(@_) if debug; ($_[0]->{b}-$_[0]->{a})}
 sub ac($)  {check(@_) if debug; ($_[0]->{c}-$_[0]->{a})}
 sub ba($)  {check(@_) if debug; ($_[0]->{a}-$_[0]->{b})}
 sub bc($)  {check(@_) if debug; ($_[0]->{c}-$_[0]->{b})}
 sub ca($)  {check(@_) if debug; ($_[0]->{a}-$_[0]->{c})}
 sub cb($)  {check(@_) if debug; ($_[0]->{b}-$_[0]->{c})}
 
 sub abc($) {check(@_) if debug; ($_[0]->{a}, $_[0]->{b}, $_[0]->{c})}
 
 sub lab($)  {check(@_) if debug; line2($_[0]->{b}, $_[0]->{a})}
 sub lac($)  {check(@_) if debug; line2($_[0]->{c}, $_[0]->{a})}
 sub lba($)  {check(@_) if debug; line2($_[0]->{a}, $_[0]->{b})}
 sub lbc($)  {check(@_) if debug; line2($_[0]->{c}, $_[0]->{b})}
 sub lca($)  {check(@_) if debug; line2($_[0]->{a}, $_[0]->{c})}
 sub lcb($)  {check(@_) if debug; line2($_[0]->{b}, $_[0]->{c})}
 
 

clone

Create a triangle from another triangle

 sub clone($)
  {my ($t) = check(@_); # Triangle   
   bless {a=>$t->a, b=>$t->b, c=>$t->c};
  }
 
 

permute

Cyclically permute the points of a triangle

 sub permute($)
  {my ($t) = check(@_); # Triangle   
   bless {a=>$t->b, b=>$t->c, c=>$t->a};
  }
 
 

center

Center

 sub center($)
  {my ($t) = check(@_); # Triangle   
   ($t->a + $t->b + $t->c) / 3;
  }
 
 

area

Area

 sub area($)
  {my ($t) = check(@_); # Triangle   
   sqrt((($t->ab*$t->ab) * ($t->ac*$t->ac)) - ($t->ab * $t->ac))/2;
  }
 
 

add

Add a vector to a triangle

 sub add($$)
  {my ($t) =          check(@_[0..0]); # Triangle   
   my ($v) = vector2Check(@_[1..1]); # Vector     
   new($t->a+$v, $t->b+$v, $t->c+$v);                         
  }
 
 

subtract

Subtract a vector from a triangle

 sub subtract($$)
  {my ($t) =          check(@_[0..0]); # Triangle   
   my ($v) = vector2Check(@_[1..1]); # Vector     
   new($t->a-$v, $t->b-$v, $t->c-$v);                         
  }
 
 

multiply

Multiply a triangle by a scalar

 sub multiply($$)
  {my ($t) = check(@_[0..0]); # Triangle   
   my ($s) =       @_[1..1] ; # Scalar     
   new($t->a * $s, $t->b * $s, $t->c * $s);                         
  }
 
 

divideBy

Divide a triangle by a scalar

 sub divideBy($$)
  {my ($t) = check(@_[0..0]); # Triangle   
   my ($s) =       @_[1..1] ; # Scalar
   $s != 0 or confess "Attempt to divide by zero";    
   new($t->a / $s, $t->b / $s, $t->c / $s);                         
  }
 
 

print

Print triangle

 sub print($)
  {my ($t) = @_; # Triangle   
   check(@_) if debug;   
   my ($a, $b, $c) = ($t->a, $t->b, $t->c);
   "triangle2($a, $b, $c)";
  }
 
 

convertSpaceToPlane

Convert space to plane coordinates

 sub convertSpaceToPlane($$)
  {my ($t, $p) = @_;
            check(@_[0..0]) if debug; # Triangle  
   vector2Check(@_[1..1]) if debug; # Vector
    
   my $q = $p-$t->a;
 
   vector2
    ($q * $t->ab / ($t->ab * $t->ab),
     $q * $t->ac / ($t->ac * $t->ac),
    );
  }
 
 

containsPoint

Check whether point p is completely contained within triangle t.

 sub containsPoint($$)
  {my ($t, $p) = @_;
            check(@_[0..0]) if debug; # Triangle  
   vector2Check(@_[1..1]) if debug; # Vector
 
   my $s = matrix2New2v($t->ab, $t->ac) / ($p - $t->a);
                  
   return 1 if 0 <= $s->x and $s->x <= 1
           and 0 <= $s->y and $s->y <= 1
           and        $s->x + $s->y <= 1;
   0;
  }
 
 

contains

Check whether triangle T is completely contained within triangle t.

 sub contains($$)
  {my ($t, $T) = @_; 
   check(@_) if debug; # Triangles
 
   return 1 if $t->containsPoint($T->a) and
               $t->containsPoint($T->b) and
               $t->containsPoint($T->c);   
   0;
  }
 
 

pointsInCommon

Find points in common to two triangles. A point in common is a point on the border of one triangle touched by the border of the other triangle.

 sub pointsInCommon($$)
  {my ($t, $T) = @_; 
   check(@_) if debug; # Triangles
 
   return ($T->a, $T->b, $T->c) if $t->contains($T);
   return ($t->a, $t->b, $t->c) if $T->contains($t);
 
   my @p = ();
   push @p, $t->a if $T->containsPoint($t->a);  
   push @p, $t->b if $T->containsPoint($t->b);  
   push @p, $t->c if $T->containsPoint($t->c);
 
   push @p, $T->a if $t->containsPoint($T->a);  
   push @p, $T->b if $t->containsPoint($T->b);  
   push @p, $T->c if $t->containsPoint($T->c);
   
   push @p, $t->lab->intersect($T->lab) if $t->lab->crossOver($T->lab); 
   push @p, $t->lab->intersect($T->lac) if $t->lab->crossOver($T->lac); 
   push @p, $t->lab->intersect($T->lbc) if $t->lab->crossOver($T->lbc); 
   push @p, $t->lac->intersect($T->lab) if $t->lac->crossOver($T->lab); 
   push @p, $t->lac->intersect($T->lac) if $t->lac->crossOver($T->lac); 
   push @p, $t->lac->intersect($T->lbc) if $t->lac->crossOver($T->lbc);
   push @p, $t->lbc->intersect($T->lab) if $t->lbc->crossOver($T->lab); 
   push @p, $t->lbc->intersect($T->lac) if $t->lbc->crossOver($T->lac); 
   push @p, $t->lbc->intersect($T->lbc) if $t->lbc->crossOver($T->lbc);
 
 # Remove duplicate points caused by splitting the vertices - inefficient and unreliable
   my %p;
   $p{"$_"}=$_ for(@p);
   values(%p); 
  }
 
 

ring

Ring of points formed by overlaying triangle t and T

 sub ring($$)
  {my ($t, $T) = @_; 
   check(@_) if debug; # Triangles
 
   my @p = $t->pointsInCommon($T);
 # scalar(@p) == 1 and warn "Only one point in common";
 # scalar(@p) == 2 and warn "Only two points in common";
   return () unless scalar(@p) > 2;
 
 # Find center
   my $c = vector2(0,0);
   $c += $_ for(@p);
   $c /= scalar(@p);
 
 # Split by y coord   
   my (@yp, @yn);
   for my $p(0..@p-1)
    {return () if ($p[$p]-$c)->length < $accuracy;
     if (($p[$p]-$c)->y >= 0)
      {push @yp, $p;
      }
     else
      {push @yn, $p;
      }
    }
 
   @yp = sort {($p[$a]-$c)->norm->x <=> ($p[$b]-$c)->norm->x} @yp;
   @yn = sort {($p[$b]-$c)->norm->x <=> ($p[$a]-$c)->norm->x} @yn;
 
   my @a;
   push @a, $p[$_] for(@yp);
   push @a, $p[$_] for(@yn);
   @a;
  }
 
 

convertPlaneToSpace

Convert plane to space coordinates

 sub convertPlaneToSpace($$)
  {my ($t, $p) = @_;                               
            check(@_[0..0]) if debug; # Triangle  
   vector2Check(@_[1..1]) if debug; # Vector in plane
    
   $t->a + ($p->x * $t->ab) + ($p->y * $t->ac);
  }
 
 

split

Split a triangle into 4 sub triangles unless the sub triangles would be too small

 sub split($$)
  {my ($t) = check(@_[0..0]); # Triangles 
   my ($s) =      (@_[1..1]); # Minimum size 
 
   return () unless
     $t->ab->length > $s and
     $t->ac->length > $s and
     $t->bc->length > $s;
 
    (new($t->a, ($t->a+$t->b)/2, ($t->a+$t->c)/2),
     new($t->b, ($t->b+$t->a)/2, ($t->b+$t->c)/2),
     new($t->c, ($t->c+$t->a)/2, ($t->c+$t->b)/2),
     new(($t->a+$t->b)/2, ($t->a+$t->b)/2, ($t->b+$t->c)/2)
    )
  } 
 
 

equals

Compare two triangles for equality

 sub equals($$)
  {my ($a, $b) = check(@_); # Triangles
   my ($aa, $ab, $ac) = ($a->a, $a->b, $a->c);
   my ($ba, $bb, $bc) = ($b->a, $b->b, $b->c);
   my  $d             = $accuracy;  
 
   return 1 if 
 abs(($aa-$ba)->length) < $d and abs(($ab-$bb)->length) < $d and abs(($ac-$bc)->length) < $d or
 abs(($aa-$ba)->length) < $d and abs(($ab-$bc)->length) < $d and abs(($ac-$bb)->length) < $d or
 abs(($aa-$bb)->length) < $d and abs(($ab-$bc)->length) < $d and abs(($ac-$ba)->length) < $d or
 abs(($aa-$bb)->length) < $d and abs(($ab-$ba)->length) < $d and abs(($ac-$bc)->length) < $d or
 abs(($aa-$bc)->length) < $d and abs(($ab-$ba)->length) < $d and abs(($ac-$bb)->length) < $d or
 abs(($aa-$bc)->length) < $d and abs(($ab-$bb)->length) < $d and abs(($ac-$ba)->length) < $d;  
   0;
  } 
 
 

Operators

Operator overloads

 use overload
  '+',       => \&add3,      # Add a vector
  '-',       => \&sub3,      # Subtract a vector
  '*',       => \&multiply3, # Multiply by a scalar
  '/',       => \&divide3,   # Divide by a scalar
  '=='       => \&equals3,   # Equals
  '""'       => \&print3,    # Print
  'fallback' => FALSE;
 
 

add

Add operator.

 sub add3
  {my ($a, $b, $c) = @_;
   return $a->add($b);
  }
 
 

subtract

Subtract operator.

 sub sub3
  {my ($a, $b, $c) = @_;
   return $a->subtract($b);
  }
 
 

multiply

Multiply operator.

 sub multiply3
  {my ($a, $b) = @_;
   return $a->multiply($b);
  }
 
 

divide

Divide operator.

 sub divide3
  {my ($a, $b, $c) = @_;
   return $a->divideBy($b);
  }
 
 

equals

Equals operator.

 sub equals3
  {my ($a, $b, $c) = @_;
   return $a->equals($b);
  }
 
 

print

Print a triangle

 sub print3
  {my ($a) = @_;
   return $a->print;
  }
 
 

Exports

Export "triangle2", "new", "newnnc", "newV", "newVnnc"

 use Math::Zap::Exports qw(
   triangle2 ($$$)
   new       ($$$)
   newnnc    ($$$)
   newV      ($$$)
   newVnnc   ($$$)
  );
 
 #_ Triangle2 ___________________________________________________________
 # Package loaded successfully
 #_______________________________________________________________________
 
 1;
 
 
 

Credits

Author

philiprbrenan@yahoo.com

philiprbrenan@yahoo.com, 2004

License

Perl License.