public Vector2? Intersects(CollisionPolygon other)
{
return TestForIntersection(this, other);
}
public static Projection ProjectPolygonOntoAxis(CollisionPolygon polygon, Vector2 axis)
{
float min = float.PositiveInfinity;
float max = float.NegativeInfinity;
foreach (Vector2 vertex in polygon.VertexList)
{
float value = Vector2.Dot(vertex, axis);
min = Math.Min(min, value);
max = Math.Max(max, value);
}
return new Projection(min, max);
}
// uses the separating axis theorem to look for a collision between these two polygons
// this will only work if the polygons are convex. Do not use concave polygons.
// Instead, decompose concave polygons into a composition of convex polygons.
//
// if there is no collision, null is returned
// otherwise, the minimum transport vector to get out of the collision is returned
// the minimum transport vector is intended to move polygon1 away from polygon2
public static Vector2? TestForIntersection(CollisionPolygon polygon1, CollisionPolygon polygon2)
{
float transportMagnitude = float.PositiveInfinity;
Vector2? transportAxis = null;
foreach (Vector2 axis in polygon1.AxesList)
{
Projection projection1 = ProjectPolygonOntoAxis(polygon1, axis);
Projection projection2 = ProjectPolygonOntoAxis(polygon2, axis);
//If there is no overlap, we can conclude the polygons do not intersect
if (!projection1.OverlapsWith(projection2))
return null;
float o = projection1.CalculateOverlap(projection2);
if (o < transportMagnitude)
{
transportMagnitude = o;
transportAxis = axis;
}
}
foreach (Vector2 axis in polygon2.AxesList)
{
Projection projection1 = ProjectPolygonOntoAxis(polygon1, axis);
Projection projection2 = ProjectPolygonOntoAxis(polygon2, axis);
//If there is no overlap, we can conclude the polygons do not intersect
if (!projection1.OverlapsWith(projection2))
return null;
float o = projection1.CalculateOverlap(projection2);
if (o < transportMagnitude)
{
transportMagnitude = o;
transportAxis = axis;
}
}
return transportMagnitude * transportAxis;
}