Ray-casting algorithm: Difference between revisions

=={{header|J}}==

<lang j>

NB.*crossPnP v point in closed polygon, crossing number

NB. bool=. points crossPnP polygon

crossPnP=: 4 : 0"2

'X Y'=. |:x

'x0 y0 x1 y1'=. |:2 ,/\^:(2={:@$@]) y

p1=. ((y0<:/Y)*. y1>/Y) +. (y0>/Y)*. y1<:/Y

p2=. (x0-/X) < (x0-x1) * (y0-/Y) % (y0 - y1)

2|+/ p1*.p2

)

</lang>

Sample data:

<lang j>

SQUAREV=: 0 0 , 10 0 , 10 10 ,: 0 10

SQUAREV=: SQUAREV, 2.5 2.5 , 7.5 0.1 , 7.5 7.5 ,: 2.5 7.5

ESAV=: 3 0 , 7 0 , 10 5 , 7 10 , 3 10 ,: 0 5

ESA=: (0 1,1 2,2 3,3 4,4 5,:5 0) , .{ ESAV

SQUARE=: (0 1,1 2,2 3,:3 0) , .{ SQUAREV

SQUAREHOLE=: (0 1,1 2,2 3,3 0,4 5,5 6,6 7,:7 4) , .{ SQUAREV

STRANGE=: (0 4,4 3,3 7,7 6,6 2,2 1,1 5,:5 0) , .{ SQUAREV

POINTS=: 5 5,5 8,2 2,0 0,10 10,2.5 2.5,0.01 5,2.2 7.4,0 5,10 5,:_4 10

</lang>

Testing:

<lang j>

(<POINTS) crossPnP every ESA;SQUARE;SQUAREHOLE;STRANGE

1 1 1 0 0 1 1 1 0 1 0

1 1 1 0 0 1 1 1 0 1 0

0 1 1 0 0 1 1 1 0 1 0

1 0 0 0 0 0 0 1 0 1 0

</lang>