// Check if this polygon intersects with another
public new bool IntersectsWith(ConvexPolygon polygon)
{
// Suppose we have two polygons, A and B. Let e be an arbitrary edge of
// polygon A or B, a be the unit vector perpendicular to e, and pA and pB
// be the projections of polygons A and B onto a. If there exists an
// edge e such that pA intersect pB is empty, then the polygons are not
// overlapping.
// Entry logging
#if IS_LOGGING_METHODS
Log.Write(String.Format("Entering method for {0}", this.Name));
#endif
// Initialize result as true
bool result = true;
#region [1] Broad phase: Bounding box test
// If the polygons' bounding boxes do not intersect, then surely the
// polygons themselves do not either
if (!this.MinBoundingBox.IntersectsWith(polygon.MinBoundingBox))
{
result = false; goto exit;
}
#endregion
#region [2] Narrow phase: SAT test
// Initialize pastSlopes list
List <float> pastSlopes = new List <float>();
// Count this polygon's vertices
int n = this.Vertices.Count;
// Count other polygon's vertices
int m = polygon.Vertices.Count;
// Get this polygon's edges
List <LineSegment> edgesA = this.Edges;
// Get other polygon's edges
List <LineSegment> edgesB = polygon.Edges;
// Loop through edges
for (int i = 0; i < n + m; i++)
{
// Point to current edge
LineSegment edge;
if (i < n)
{
edge = edgesA[i];
}
else
{
edge = edgesB[i - n];
}
// Get edge's unit normal vector, i.e. the 'axis'
Vector2 axis = (edge.Point2 - edge.Point1).Unit.Normal;
// Get axis slope
float slope = axis.Slope;
// Initialize slopeAlreadyTested as false
bool slopeAlreadyTested = false;
// Check if former iteration already checked this slope
for (int j = 0; j < pastSlopes.Count; j++)
{
if (slope == pastSlopes[j])
{
slopeAlreadyTested = true; break;
}
}
// If slopeAlreadyTested, then skip this iteration
if (slopeAlreadyTested)
{
continue;
}
// Remember this slope for future iterations
pastSlopes.Add(slope);
// Project polygons onto axis
Interval projectionA = this.ProjectOnto(axis);
Interval projectionB = polygon.ProjectOnto(axis);
// Check if their projections intersect
if (!projectionA.IntersectsWith(projectionB))
{
// If not, then the polygons do not intersect
result = false; goto exit;
}
}
#endregion
// [*] Exit trap
exit:
// Exit logging
#if IS_LOGGING_METHODS
Log.Write(String.Format("Exiting method for {0}", this.Name));
#endif
// Return result
return(result);
}
