Here's some code that finds whether a particular point is inside a polygon.
Actual routine is not mine, I've found the C code online (http://www.visibone.com/inpoly/inpoly.c) and translated it into GLB.
It's great for implementing various regions, zones, collision or whatever else into your programs.
Code is pure math, it has nothing to do with graphical polygons (no acceleration) but it supports all kinds of mad polygonal shapes.
SYSTEMPOINTER TRUE
//create polygon
LOCAL poly[]
DIM poly[RND(3)+3][2]
FOR i = 0 TO BOUNDS(poly[], 0) - 1
poly[i][0] = RND(640)
poly[i][1] = RND(480)
NEXT
// main loop
WHILE TRUE
LOCAL mx,my,mba,mbb
MOUSESTATE mx, my, mba, mbb
drawPoly(poly[])
IF inPoly(poly[], mx, my)
PRINT "Inside!",0,0
ENDIF
SHOWSCREEN
WEND
FUNCTION inPoly: poly[], tx, ty
LOCAL newx, newy, oldx, oldy
LOCAL x1, y1, x2, y2
LOCAL inside
LOCAL npoints = BOUNDS(poly[], 0)
IF npoints < 3 THEN RETURN 0
oldx = poly[npoints - 1][0]
oldy = poly[npoints - 1][1]
FOR i = 0 TO npoints - 1
newx = poly[i][0]
newy = poly[i][1]
IF newx > oldx
x1 = oldx
x2 = newx
y1 = oldy
y2 = newy
ELSE
x1 = newx
x2 = oldx
y1 = newy
y2 = oldy
ENDIF
IF ((newx < tx) = (tx <= oldx) AND (ty-y1)*(x2-x1) < (y2-y1)*(tx-x1))
inside = NOT inside
ENDIF
oldx = newx
oldy = newy
NEXT
RETURN inside
ENDFUNCTION
FUNCTION drawPoly: poly[]
LOCAL npoints = BOUNDS(poly[], 0)
FOR i = 0 TO npoints-2
DRAWLINE poly[i][0],poly[i][1], poly[i+1][0],poly[i+1][1], RGB(200,200,200)
NEXT
DRAWLINE poly[-1][0],poly[-1][1], poly[0][0],poly[0][1], RGB(200,200,200)
ENDFUNCTION
Nice :)
Thank you for sharing.
Cool. Looks faster than the code I'd converted from http://www.vb-helper.com/howto_find_angles.html
TYPE _vertex
pts[] // polygon
x
y
z
width
height
off_x
off_y
ENDTYPE
FUNCTION PointInPolygon: ply AS _vertex, point AS _vertex
LOCAL c, corners, total_angle
LOCAL ver AS _vertex
corners = BOUNDS(ply.pts[], 0) - 1
total_angle = GetAngleProduct(ply.pts[corners][0], ply.pts[corners][1], point.x, point.y, ply.pts[0][0], ply.pts[0][1])
FOR c = 0 TO corners - 1
ver.x = ply.pts[c][0] + ply.x
ver.y = ply.pts[c][1] + ply.y
ver.off_x = point.x
ver.off_y = point.y
ver.width = ply.pts[c + 1][0] + ply.x
ver.height = ply.pts[c + 1][1] + ply.y
total_angle = total_angle + GetAngleProduct(ver.x, ver.y, ver.off_x, ver.off_y, ver.width, ver.height)
NEXT
RETURN ABS(INTEGER(total_angle))
ENDFUNCTION
FUNCTION GetAngleProduct: Ax,Ay,Bx,By,Cx,Cy
LOCAL dot_product, cross_product
dot_product = DotProduct(Ax, Ay, Bx, By, Cx, Cy)
cross_product = CrossProductLength(Ax, Ay, Bx, By, Cx, Cy)
RETURN ATan2(cross_product, dot_product)
ENDFUNCTION
FUNCTION ATan2: opp,adj
LOCAL angle
LOCAL iPI = 3.14159265358979323846
IF ABS(adj) < 0.0001
angle = iPI / 2
ELSE
angle = ABS(ATAN(opp, adj))
ENDIF
IF adj < 0
angle = iPI - angle
ENDIF
IF opp < 0
angle = -angle
ENDIF
RETURN angle
ENDFUNCTION
FUNCTION CrossProductLength: Ax,Ay,Bx,By,Cx,Cy
LOCAL BAx=Ax-Bx
LOCAL BAy=Ay-By
LOCAL BCx=Cx-Bx
LOCAL BCy=Cy-By
RETURN (BAx*BCy) - (BAy*BCx)
ENDFUNCTION
FUNCTION DotProduct: Ax,Ay,Bx,By,Cx,Cy
LOCAL BAx= Ax - Bx
LOCAL BAy= Ay - By
LOCAL BCx= Cx - Bx
LOCAL BCy= Cy - By
RETURN (BAx*BCx) + (BAy*BCy)
ENDFUNCTION
Cheers me dears. I was just about to write a routine to do this myself. Now I won't have to. :)
Perfect. Just what I was looking for :)
Many thanks.
Thanks -domius very interesting the code, perhaps for void make a for over a huge mesh can works fine?¿...
Thanks I think I use your code in my simple 3D Editor... :booze: