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Is point inside a convex shape?

/ Published in: ActionScript 3
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The convex polygon algorithm, which, as the name says, only works for convex polygons and is based on whether or not a point is on a certain “side” of every edge of the polygon.

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  1. public function isPointInsideShape(_point:Vector3D, _shapeVerices:Vector.<Vector3D>):Boolean
  2. {
  3. 	var _numberOfSides:int = shapeVertices.length;
  4. 	var _i:int = 0;
  5. 	var _leftOrRightSide:Boolean = false;
  6. 	var _firstEdgePoint:Vector3D = null;
  7. 	var _secondEdgePoint:Vector3D = null;
  8.  
  9. 	while(_i < _numberOfSides)
  10. 	{
  11. 		_firstEdgePoint = _shapeVertices[_i];
  12. 		_secondEdgePoint = _shapeVertices[(_i + 1) % _numberOfSides];
  13.  
  14. 		if(_i == 0){
  15. 			// Determining if the point is to the left or to the right of first edge true for left, false for right
  16. 			_leftOrRightSide = ((_point.y - _firstEdgePoint.y) * (_secondEdgePoint.x - _firstEdgePoint.x)) - ((_point.x - _firstEdgePoint.x) * (_secondEdgePoint.y - _firstEdgePoint.y)) > 0;
  17. 		}
  18. 		else
  19. 		{
  20. 			// Now all edges must be on the same side
  21. 			if(_leftOrRightSide && ((_point.y - _firstEdgePoint.y) * (_secondEdgePoint.x - _firstEdgePoint.x)) - ((_point.x - _firstEdgePoint.x) * (_secondEdgePoint.y - _firstEdgePoint.y)) < 0)
  22. 			{
  23. 				// Not all edges are on the same side! 
  24. 				return false;
  25. 			}
  26. 			else if(!_leftOrRightSide && ((_point.y - _firstEdgePoint.y) * (_secondEdgePoint.x - _firstEdgePoint.x)) - ((_point.x - _firstEdgePoint.x) * (_secondEdgePoint.y - _firstEdgePoint.y)) > 0)
  27. 			{
  28. 				// Not all edges are on the same side!
  29. 				return false;
  30. 			}
  31. 		}
  32. 		_i++;
  33. 	}
  34.  
  35. 	// We looped through all vertices and didn't detect different sides
  36. 	return true;
  37. }

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