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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Ray-casting-algorithm/REXX/ray-casting-algorithm.rexx Normal file
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/*REXX program verifies if a horizontal ray from point P intersects a polygon. */
call points 5 5, 5 8, -10 5, 0 5, 10 5, 8 5, 10 10
A= 2.5; B= 7.5 /* ◄───── used for shorter arguments (below).*/
call poly 0 0, 10 0, 10 10, 0 10 ; call test 'square'
call poly 0 0, 10 0, 10 10, 0 10, A A, B A, B B, A B ; call test 'square hole'
call poly 0 0, A A, 0 10, A B, B B, 10 10, 10 0 ; call test 'irregular'
call poly 3 0, 7 0, 10 5, 7 10, 3 10, 0 5 ; call test 'hexagon'
exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
in$out: procedure expose point. poly.; parse arg p; #= 0
do side=1 to poly.0 by 2; #= # +intersect(p, side); end /*side*/
return # // 2 /*ODD is inside. EVEN is outside.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
intersect: procedure expose point. poly.; parse arg ?,s; sp= s + 1
epsilon= '1e' || (-digits() % 2)
Px= point.?.x; Ax= poly.s.x; Bx= poly.sp.x
Py= point.?.y; Ay= poly.s.y; By= poly.sp.y /* [↓] do vertex swap.*/
if Ay>By then parse value Ax Ay Bx By with Bx By Ax Ay
if Py=Ay | Py=By then Py= Py + epsilon
if Py<Ay | Py>By | Px>max(Ax, Bx) then return 0
if Px<min(Ax, Bx) then return 1
if Ax\=Bx then red = (By-Ay) / (Bx-Ax)
else red = i"1e" || (digits() *2) /* ◄─── infinity.*/
if Ax\=Px then return (Py-Ay) / (Px-Ax) >= red
else return 1
/*──────────────────────────────────────────────────────────────────────────────────────*/
points: wx= 0; wy= 0; do j=1 for arg(); parse value arg(j) with xx yy
wx= max(wx, length(xx) ); call value 'POINT.'j".X", xx
wy= max(wy, length(yy) ); call value 'POINT.'j".Y", yy
end /*j*/
call value point.0, j-1 /*define the number of points. */
return /* [↑] adjust J (for DO loop)*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
poly: @= 'POLY.'; parse arg Fx Fy /* [↓] process the X,Y points.*/
n= 0
do j=1 for arg(); n= n + 1; parse value arg(j) with xx yy
call value @ || n'.X', xx ; call value @ || n".Y", yy
if n//2 then iterate; n= n + 1 /*Inside? Then skip this point.*/
call value @ || n'.X', xx ; call value @ || n".Y", yy
end /*j*/
n= n + 1 /*POLY.0 is # segments(sides).*/
call value @ || n'.X', Fx; call value @ || n".Y", Fy; call value @'0', n
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
test: say; do k=1 for point.0; w= wx + wy + 2 /*W, WX, WY ≡are various widths*/
say right(' ['arg(1)"] point:", 30),
right( right(point.k.x, wx)', 'right(point.k.y, wy), w) " is ",
right( word('outside inside', in$out(k) + 1), 7)
end /*k*/
return /* [↑] format the output nicely*/