Clockwise sort of coordinates

[Albert Richheimer]

You mean this one, from Stuart Mclachlan, Sept. 28, 2022?

Code:

#COMPILE EXE
#DIM ALL
MACRO RadToDeg(r) = (r * 57.2957795130823209##)
MACRO Pi = 3.14159265358979324##
MACRO TwoPi = 6.283185307179586##

TYPE CartPt
    s AS EXT 'sequence number
    x AS EXT ' x coord
    y AS EXT ' y coord
    a AS EXT  'angle in degrees about centre
    d AS EXT 'distance from centre
END TYPE

GLOBAL TotPoints AS LONG
GLOBAL Minx AS EXT
GLOBAL Maxx AS EXT
GLOBAL Miny AS EXT
GLOBAL MaxY AS EXT

FUNCTION PBMAIN() AS LONG
    LOCAL hGrf AS DWORD
    LOCAL x AS LONG
    LOCAL CentreX, CentreY,OffsetX,OffsetY,SumX,SumY AS EXT

'Set parameters
    totpoints = 20
    minx = 20
    miny = 50
    maxx = 260
    maxy = 160

'Initialise a random set of points
    DIM pts(1 TO TotPoints) AS CartPt
    RANDOMIZE TIMER
    FOR x = 1 TO TotPoints
        pts(x).s = x
        pts(x).x = RND() * (Maxx - minx) + minx
        pts(x).Y = RND() * (Maxy - miny) + miny
        SumX += pts(x).x
        SumY += pts(x).y
    NEXT
    CentreX = SumX/TotPoints
    CentreY = SumY/TotPoints

'Calculate polar coordinate from Centre point
    FOR x = 1 TO TotPoints
        OffsetX = pts(x).x - CentreX
        Offsety = pts(x).y - Centrey
        pts(x).a = ATN(Offsety / Offsetx) ' if you want to use degrees: RadToDeg(ATN(Offsety / Offsetx))
        IF Offsetx < 0 THEN 'Quadrant 2 or 3
            pts(x).a += Pi '180 if RadToDeg
        ELSEIF Offsety < 0 THEN ' Quadrant 4
                pts(x).a += TwoPi '360  if RadToDeg
        END IF
        pts(x).d = SQR(Offsety ^ 2 + offsetx ^ 2)
     NEXT

     ARRAY SORT pts(), CALL SortClockwise

     GRAPHIC WINDOW NEW "Points - Hit any key to cycle and exit", 50,50,600,600 TO hGrf
     GRAPHIC WINDOW STABILIZE
     GRAPHIC SCALE (minx,miny) - (maxx,maxy)

     PlotPoints Pts()
     GRAPHIC WAITKEY$
     DrawPoly(Pts(),CentreX,CentreY)
     GRAPHIC WAITKEY$
     GRAPHIC PAINT  BORDER(CentreX,CentreY) , %RGB_GREEN, %RGB_BLACK
     GRAPHIC WAITKEY$
     Radiate(Pts(),CentreX,CentreY)
     GRAPHIC WAITKEY$

     GRAPHIC WINDOW END
END FUNCTION

FUNCTION SortClockwise(p1 AS Cartpt,p2 AS Cartpt) AS LONG
     IF p1.a < p2.a THEN FUNCTION = -1 : EXIT FUNCTION
     IF p1.a > p2.a THEN FUNCTION =  1 : EXIT FUNCTION
     'same angle - sort "inside" one first
     IF p1.d < p2.d THEN FUNCTION =  1 : EXIT FUNCTION
     IF p1.d > p2.d THEN FUNCTION =  -1 : EXIT FUNCTION
END FUNCTION

FUNCTION Radiate(pts() AS cartPt,cx AS EXT, cy AS EXT )AS LONG
     LOCAL x AS LONG
     FOR x = LBOUND(pts()) TO UBOUND(pts())
         GRAPHIC LINE (cx,cy) - (pts(x).x,pts(x).y),%RGB_WHITE
     NEXT
END FUNCTION

FUNCTION PlotPoints(pts() AS CartPt) AS LONG
    LOCAL x AS LONG
    LOCAL xsize,ysize AS EXT
    xsize = (maxx-minx)/200
    ysize = (maxy-miny)/200
    FOR x = LBOUND(pts()) TO UBOUND(pts())
       GRAPHIC ELLIPSE (pts(x).x -xsize,pts(x).y-ysize) - (pts(x).x+xsize,pts(x).y+ysize),%RGB_RED,%RGB_RED
    NEXT
END FUNCTION

FUNCTION DrawPoly(pts() AS CartPt,cx AS EXT,cy AS EXT) AS LONG
    LOCAL x AS LONG
'If wanted, mark the centre of the polygon
    GRAPHIC SET POS (cX,cY)
    GRAPHIC PRINT "X"
'Now draw it
    GRAPHIC SET POS (pts(LBOUND(pts())).x,pts(LBOUND(pts())).y)
    FOR x = LBOUND(pts()) + 1 TO UBOUND(pts())
       GRAPHIC LINE (pts(x-1).x,pts(x-1).y)- (pts(x).x,pts(x).y)
    NEXT
    GRAPHIC LINE (pts(UBOUND(pts())).x,pts(UBOUND(pts())).y) - (pts(LBOUND(pts())).x,pts(LBOUND(pts())).y)
END FUNCTION
'

You will find it in Gary Beene's gbthreads.