Geometry in Pascal: what changed
Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.
Title: Geometry in Pascal
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| 1 | + | ## Checking if a point is inside a polygon (integer version) | |
| 2 | + | ||
| 3 | + | ``` pascal | |
| 4 | + | // The function will return True if the point x,y is inside the polygon, or | |
| 5 | + | // False if it is not. | |
| 6 | + | // | |
| 7 | + | // Original C code: http://www.visibone.com/inpoly/inpoly.c.txt | |
| 8 | + | // | |
| 9 | + | // Translation from C by Felipe Monteiro de Carvalho | |
| 10 | + | // | |
| 11 | + | // License: Public Domain | |
| 12 | + | function IsPointInPolygon(AX, AY: Integer; APolygon: array of TPoint): Boolean; | |
| 13 | + | var | |
| 14 | + | xnew, ynew: Cardinal; | |
| 15 | + | xold,yold: Cardinal; | |
| 16 | + | x1,y1: Cardinal; | |
| 17 | + | x2,y2: Cardinal; | |
| 18 | + | i, npoints: Integer; | |
| 19 | + | inside: Integer = 0; | |
| 20 | + | begin | |
| 21 | + | Result := False; | |
| 22 | + | npoints := Length(APolygon); | |
| 23 | + | if (npoints < 3) then Exit; | |
| 24 | + | xold := APolygon[npoints-1].X; | |
| 25 | + | yold := APolygon[npoints-1].Y; | |
| 26 | + | for i := 0 to npoints - 1 do | |
| 27 | + | begin | |
| 28 | + | xnew := APolygon[i].X; | |
| 29 | + | ynew := APolygon[i].Y; | |
| 30 | + | if (xnew > xold) then | |
| 31 | + | begin | |
| 32 | + | x1:=xold; | |
| 33 | + | x2:=xnew; | |
| 34 | + | y1:=yold; | |
| 35 | + | y2:=ynew; | |
| 36 | + | end | |
| 37 | + | else | |
| 38 | + | begin | |
| 39 | + | x1:=xnew; | |
| 40 | + | x2:=xold; | |
| 41 | + | y1:=ynew; | |
| 42 | + | y2:=yold; | |
| 43 | + | end; | |
| 44 | + | if (((xnew < AX) = (AX <= xold)) // edge "open" at left end | |
| 45 | + | and ((AY-y1)*(x2-x1) < (y2-y1)*(AX-x1))) then | |
| 46 | + | begin | |
| 47 | + | inside := not inside; | |
| 48 | + | end; | |
| 49 | + | xold:=xnew; | |
| 50 | + | yold:=ynew; | |
| 51 | + | end; | |
| 52 | + | Result := inside <> 0; | |
| 53 | + | end; | |
| 54 | + | ``` | |
| 55 | + | ||
| 56 | + | ## Checking if a point is inside a polygon, version 2 | |
| 57 | + | ||
| 58 | + | Code from [German forum](https://www.lazarusforum.de/viewtopic.php?p=118119#p118119), by winni. | |
| 59 | + | ||
| 60 | + | ``` pascal | |
| 61 | + | function PointInPoly(p : TPointF; const poly : array of TPointF) : Boolean; | |
| 62 | + | var | |
| 63 | + | i,k : integer; | |
| 64 | + | Begin | |
| 65 | + | result := false; | |
| 66 | + | k := High(poly); | |
| 67 | + | For i := 0 to high(poly) do begin | |
| 68 | + | if ( | |
| 69 | + | ( ((poly[i].y <= p.y) and (p.y < poly[k].y)) or ((poly[k].y <= p.y) and (p.y < poly[i].y)) ) and | |
| 70 | + | (p.x < ((poly[k].x - poly[i].x) * (p.y - poly[i].y) / (poly[k].y - poly[i].y) + poly[i].x) ) | |
| 71 | + | ) then result := not result; | |
| 72 | + | k := i | |
| 73 | + | end; | |
| 74 | + | end; | |
| 75 | + | ``` | |
| 76 | + | ||
| 77 | + | ## See also | |
| 78 | + | ||
| 79 | + | - [A Point about Polygons](http://www.visibone.com/inpoly/) | |
| 80 | + | ||
| 81 | + | --- | |
| 82 | + | *From the Free Pascal wiki, page "Geometry in Pascal", as it stood on 2022-03-09 after a change by Alextp, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).* |