Revision as of 23:25, 9 December 2009

Function: integer isPointInPolygon2D( list polygon, vector point );

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

• list	polygon	–	A polygon described as a list of 2D vectors for its points in around the edge order.
• vector	point	–	The point to test for, described by a 2D vector (a vector using only the x and y values)

It is possible (and fairly easy) to adapt this function to use a list of paired floats, both implementations are provided.

Caveats

the polygon MAY need to be a shape that can be built with triangles, it's unclear from the original if this is a requirement.
0,0 should NOT be a regular point on the polygon list. See notes below.

Examples

<lsl>if (isPointInPolygon2D( [<1,1,0>, <1,2,0>, <2,2,0>, <2,1,0>], <1.5,1.5,0> )){ llOwnerSay( "Point is in polygon" ); }else{ llOwnerSay( "Point is not in polygon" ); }</lsl> <lsl>if (isPointInPolygon2D_XY( [<1,1,0>, <1,2,0>, <2,2,0>, <2,1,0>], 1.5, 1.5 )){ llOwnerSay( "Point is in polygon" ); }else{ llOwnerSay( "Point is not in polygon" );

}</lsl>

Notes

you can have polygons with holes, either by separating the polygon list of points into distinct parts and placing a 0,0 point after each part, or by making a two partt call to the function, that uses an outer and an inner detection polygon with the inner (cutout) overriding the outer.

Implementations

This implementation is adapted from the original found here. Please include the copyright comments below when using this code. See original page for indepth discussion of usage.

Copyright

<lsl>/*//-- LSL Port 2009 Void Singer --//*/ /*//-- Copyright (c) 1970-2003, Wm. Randolph Franklin --//*/ /* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: 1. Redistributions of source code must retain the above copyright

  notice, this list of conditions and the following disclaimers.

2. Redistributions in binary form must reproduce the above copyright notice

  in the documentation and/or other materials provided with the distribution.

3. The name of W. Randolph Franklin may not be used to endorse or promote

  products derived from this Software without specific prior written permission

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

/</lsl>

Code

Vector version: <lsl>integer isPointInPolygon2D( list vLstPolygon, vector vPosTesting ){ integer vBooInPlygn; integer vIntCounter = [] != vLstPolygon; vector vPosVertexA = llList2Vector( vLstPolygon, vIntCounter ); vector vPosVertexB;

while (vIntCounter){ vPosVertexB = vPosVertexA; vPosVertexA = llList2Vector( vLstPolygon, ++vIntCounter );

if ((vPosVertexA.y > vPosTesting.y) ^ (vPosVertexB.y > vPosTesting.y)){ if (vPosTesting.x < (vPosVertexB.x - vPosVertexA.x) * (vPosTesting.y - vPosVertexA.y) / `(vPosVertexB.y - vPosVertexA.y) + vPosVertexA.x ){ vBooInPlygn = !vBooInPlygn; } } } return vBooInPlygn; }</lsl>

Float Pair Version: <lsl>integer isPointInPolygon2D_XY( list vLstPolygonXY, float vFltTesting_X, float vFltTesting_Y ){ integer vBooInPlygnXY; integer vIntCounterXY = ([] != vLstPolygonXY); float vFltVertexA_X = llList2Float( vLstPolygonXY, -2 ); float vFltVertexA_Y = llList2Float( vLstPolygonXY, -1 ); float vFltVertexB_X; float vFltVertexB_Y;

while (vIntCounterXY){ vFltVertexB_X = vFltVertexA_X; vFltVertexB_Y = vFltVertexA_Y; vFltVertexA_X = llList2Float( vLstPolygonXY, vIntCounterXY++ ); vFltVertexA_Y = llList2Float( vLstPolygonXY, vIntCounterXY++ );

if ((vFltVertexA_Y > vFltTesting_Y) ^ (vFltVertexB_Y > vFltTesting_Y)){ if (vFltTesting_X < (vFltVertexB_X - vFltVertexA_X) * (vFltTesting_Y - vFltVertexA_Y) / `(vFltVertexB_Y - vFltVertexA_Y) + vFltVertexA_X ){ vBooInPlygnXY = !vBooInPlygnXY; } } } return vBooInPlygnXY; }</lsl>

@@ Line 5: / Line 5: @@
 |return_type=integer
 |return_text=TRUE if the point lies within the described polygon, FALSE if not
-|p1_type=vector|p1_name=point|p1_desc=The point to test for, described by a 2D vector (a vector using only the x and y values)
+|p1_type=list|p1_name=polygon|p1_desc=A polygon described as a list of 2D vectors for its points in around the edge order.
-|p2_type=list|p2_name=polygon|p2_desc=A polygon described as a list of 2D vectors for its points
+|p2_type=vector|p2_name=point|p2_desc=The point to test for, described by a 2D vector (a vector using only the x and y values)
 |mode=user
 |cat1=Examples
 |cat2=Library
-|caveats=*the polygon points list should be in around-the-edge order (direction doesn't matter), it may not work properly otherwise.
+|caveats=*the polygon MAY need to be a shape that can be built with triangles, it's unclear from the original if this is a requirement.
-*the polygon MAY need to be a shape that can be built with triangles, it's unclear from the original if this is a requirement.
+*0,0 should NOT be a regular point on the polygon list. See notes below.
-|examples=<lsl>if (isPointInPolygon2D(<0.5,0.5,0>, [<0,0,0>, <0,1,0>, <1,1,0>, <1,0,0>])) llOwnerSay("Point is in polygon");
+|notes=*you can have polygons with holes, either by separating the polygon list of points into distinct parts and placing a 0,0 point after each part, or by making a two partt call to the function, that uses an outer and an inner detection polygon with the inner (cutout) overriding the outer.
-else llOwnerSay("Point is not in polygon");</lsl>
+|examples=<lsl>if (isPointInPolygon2D( [<1,1,0>, <1,2,0>, <2,2,0>, <2,1,0>], <1.5,1.5,0> )){
+	llOwnerSay( "Point is in polygon" );
+}else{
+	llOwnerSay( "Point is not in polygon" );
+}</lsl>
+<lsl>if (isPointInPolygon2D_XY( [<1,1,0>, <1,2,0>, <2,2,0>, <2,1,0>], 1.5, 1.5 )){
+	llOwnerSay( "Point is in polygon" );
+}else{
+	llOwnerSay( "Point is not in polygon" );
+}</lsl>
 }}
 = Implementations =
-This implementation is adapted from the original found [http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html here]. Please include the copyright comments below when using this code.
+This implementation is adapted from the original found [http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html here]. Please include the copyright comments below when using this code. See original page for indepth discussion of usage.
 == Copyright ==
@@ Line 48: / Line 57: @@
 == Code ==
 Vector version:
-<lsl>integer uPointInPolygon2D( list vLstPolygon, vector vPosTesting ){
+<lsl>integer isPointInPolygon2D( list vLstPolygon, vector vPosTesting ){
 	integer vBooInPlygn;
 	integer vIntCounter = [] != vLstPolygon;
@@ Line 69: / Line 78: @@
 Float Pair Version:
-<lsl>integer uPointInPolygon2D_XY( list vLstPolygonXY, float vFltTesting_X, float vFltTesting_Y ){
+<lsl>integer isPointInPolygon2D_XY( list vLstPolygonXY, float vFltTesting_X, float vFltTesting_Y ){
 	integer vBooInPlygnXY;
 	integer vIntCounterXY = ([] != vLstPolygonXY);

Difference between revisions of "IsPointInPolygon2D"

Revision as of 23:25, 9 December 2009

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