Find if a point is within a triangle: Difference between revisions

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=={{header|Fortran}}==

<lang Fortran>

PROGRAM POINT_WITHIN_TRIANGLE

IMPLICIT NONE

REAL (KIND = SELECTED_REAL_KIND (8)) px, py, ax, ay, bx, by, cx, cy

px = 0.0

py = 0.0

ax = 1.5

ay = 2.4

bx = 5.1

by = -3.1

cx = -3.8

cy = 1.2

IF (IS_P_IN_ABC (px, py, ax, ay, bx, by, cx, cy)) THEN

WRITE (*, *) 'Point (', px, ', ', py, ') is within triangle &

[(', ax, ', ', ay,'), (', bx, ', ', by, '), (', cx, ', ', cy, ')].'

ELSE

WRITE (*, *) 'Point (', px, ', ', py, ') is not within triangle &

[(', ax, ', ', ay,'), (', bx, ', ', by, '), (', cx, ', ', cy, ')].'

END IF

CONTAINS

!Provide xy values of points P, A, B, C, respectively.

LOGICAL FUNCTION IS_P_IN_ABC (px, py, ax, ay, bx, by, cx, cy)

REAL (KIND = SELECTED_REAL_KIND (8)), INTENT (IN) :: px, py, ax, ay, bx, by, cx, cy

REAL (KIND = SELECTED_REAL_KIND (8)) :: vabx, vaby, vacx, vacy, a, b

vabx = bx - ax

vaby = by - ay

vacx = cx - ax

vacy = cy - ay

a = ((px * vacy - py * vacx) - (ax * vacy - ay * vacx)) / &

(vabx * vacy - vaby * vacx)

b = -((px * vaby - py * vabx) - (ax * vaby - ay * vabx)) / &

(vabx * vacy - vaby * vacx)

IF ((a .GT. 0) .AND. (b .GT. 0) .AND. (a + b < 1)) THEN

IS_P_IN_ABC = .TRUE.

ELSE

IS_P_IN_ABC = .FALSE.

END IF

END FUNCTION IS_P_IN_ABC

END PROGRAM POINT_WITHIN_TRIANGLE

</lang>

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Point ( 0.0000000000000000 , 0.0000000000000000 ) is within triangle [( 1.5000000000000000 , 2.4000000953674316 ), ( 5.0999999046325684 , -3.0999999046325684 ), ( -3.7999999523162842 , 1.2000000476837158 )].