isPointInPolygon2D
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Summary
Function: integer isPointInPolygon2D( vector point, list polygon );
Tests a polygon (described as a list of 2D vectors) to see if a 2D point lies within it. Useful for detecting where an event occurred within 2D space.
Returns an integer TRUE if the point lies within the described polygon, FALSE if not
| • vector | point | – | The point to test for, described by a 2D vector (a vector using only the x and y values) | |
| • list | polygon | – | A polygon described as a list of 2D vectors for its points |
It is possible (and fairly easy) to adapt this function to use a list of paired floats, both implementations are provided.
Examples
if (isPointInPolygon2D(<0.5,0.5,0>, [<0,0,0>, <0,1,0>, <1,1,0>, <1,0,0>])) llOwnerSay("Point is in polygon");
Implementations
Vectors
<lsl>integer isPointInPolygon2D(vector point, list polygon) {
integer l = polygon != [];
integer i = 0; integer j = l - 1; integer inPoly = FALSE;
vector iv; vector jv; float diffY;
while (i < l) {
iv = llList2Vector(polygon, i);
jv = llList2Vector(polygon, j);
diffY = (jv.y - iv.y);
if (diffY == 0.0) diffY = 1000.0;
if ((((iv.y <= point.y) &&
(point.y < (jv.x - iv.x) * (point.y - iv.y) / diffY + iv.x))))
inPoly = !inPoly;
j = i++;
}
return inPoly != 0;
}</lsl>
Float-pairs
<lsl>integer isPointInPolygon2D(float x, float y, list polygon) {
integer l = polygon != [];
integer i = 0; integer j = l - 2; integer inPoly = FALSE;
float ix; float iy; float jx; float jy; float diffY;
while (i < l) {
ix = llList2Float(polygon, i);
iy = llList2Float(polygon, ++i);
jx = llList2Float(polygon, j);
jy = llList2Float(polygon, ++j);
diffY = (jy - iy);
if (diffY == 0.0) diffY = 1000.0;
if ((((iy <= y) &&
(y < (jx - ix) * (y - iy) / diffY + ix))))
inPoly = !inPoly;
j = i++;
}
return inPoly != 0;
}</lsl>