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Is a point inside a given polygon?
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Question:
It is of interest to determin if a point is within a given polygon. My polygon is represented as an array of TPoints.
Answer:
A quick way to do this is to use the Windows API function PtInRegion. If not already avalaible, call CreatePolygonRgn() to create a region and pass the region's handle to PtInRegion().
Don't forget to free Windows' region handle afterwards.
A neat trick is to use the Length() function to obtain the number of points in the polygon.
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// PointInPolygon() function by Andreas Filsinger
function PointInPolygon (const x,y : integer; aPolygon: array of TPoint): boolean;
var
PolyHandle: hRgn;
begin
PolyHandle := CreatePolygonRgn(aPolygon[0], Length(aPolygon), Winding);
result := PtInRegion(PolyHandle,X,Y);
DeleteObject(PolyHandle);
end; | ||
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