public static PolygonCollisionResult PolygonCollisionResult(Polygon polygonMoving, Polygon polygon, Vector2 velocity)
{
PolygonCollisionResult result = new PolygonCollisionResult();
float minIntervalDistance = float.PositiveInfinity;
Vector2 translationAxis = Vector2.Zero;
List<Vector2> edges = new List<Vector2>(polygonMoving.Edges);
edges.AddRange(polygon.Edges);
foreach (Vector2 edge in edges)
{
// Find the axis perpendicular to the current edge
Vector2 axis = new Vector2(-edge.Y, edge.X);
axis.Normalize();
// Find the projection of the polygon on the current axis
float minPolygonMoving = 0;
float maxPolygonMoving = 0;
float minPolygon = 0;
float maxPolygon = 0;
ProjectPolygon(axis, polygonMoving, ref minPolygonMoving, ref maxPolygonMoving);
ProjectPolygon(axis, polygon, ref minPolygon, ref maxPolygon);
// Project the velocity on the current axis
float velocityProjection = VectorUtil.DotProduct(axis, velocity);
// Get the projection of polygon A during the movement
if (velocityProjection < 0)
{
minPolygonMoving += velocityProjection;
}
else
{
maxPolygonMoving += velocityProjection;
}
// Do the same test as above for the new projection
float intervalDistance = IntervalDistance(minPolygonMoving, maxPolygonMoving, minPolygon, maxPolygon);
if (intervalDistance > 0)
{
result.WillIntersect = false;
break;
}
// Check if the current interval distance is the minimum one. If so store
// the interval distance and the current distance.
// This will be used to calculate the minimum translation vector
intervalDistance = Math.Abs(intervalDistance);
if (intervalDistance < minIntervalDistance)
{
minIntervalDistance = intervalDistance;
translationAxis = axis;
Vector2 d = polygonMoving.Center - polygon.Center;
if (VectorUtil.DotProduct(d, translationAxis) < 0) translationAxis = -translationAxis;
}
}
// The minimum translation vector can be used to push the polygons appart.
// First moves the polygons by their velocity
// then move polygonA by MinimumTranslationVector.
if (result.WillIntersect) result.MinimumTranslationVector = translationAxis * minIntervalDistance;
return result;
}
// Calculate the projection of a polygon on an axis and returns it as a [min, max] interval
private static void ProjectPolygon(Vector2 axis, Polygon polygon, ref float min, ref float max)
{
// To project a point on an axis use the dot product
float temp = VectorUtil.DotProduct(axis, polygon.Points[0]);
min = temp;
max = temp;
for (int i = 0; i < polygon.Points.Count; i++)
{
temp = VectorUtil.DotProduct(polygon.Points[i], axis);
if (temp < min)
{
min = temp;
}
else
{
if (temp > max)
{
max = temp;
}
}
}
}