// Check if polygon A is going to collide with polygon B for the given velocity
public SvgCollision.PolygonCollisionResult PolygonCollision(Polygon polygonA, Polygon polygonB, Vector velocity)
{
SvgCollision.PolygonCollisionResult result = new SvgCollision.PolygonCollisionResult();
result.IsIntersecting = true;
result.WillIntersect = true;
int edgeCountA = polygonA.Edges.Count;
int edgeCountB = polygonB.Edges.Count;
float minIntervalDistance = float.PositiveInfinity;
Vector translationAxis = new Vector();
Vector edge;
// Loop through all the edges of both polygons
for (int edgeIndex = 0; edgeIndex < edgeCountA + edgeCountB; edgeIndex++) {
if (edgeIndex < edgeCountA) {
edge = polygonA.Edges[edgeIndex];
} else {
edge = polygonB.Edges[edgeIndex - edgeCountA];
}
// ===== 1. Find if the polygons are currently intersecting =====
// Find the axis perpendicular to the current edge
Vector axis = new Vector(-edge.Y, edge.X);
axis.Normalize();
// Find the projection of the polygon on the current axis
float minA = 0; float minB = 0; float maxA = 0; float maxB = 0;
ProjectPolygon(axis, polygonA, ref minA, ref maxA);
ProjectPolygon(axis, polygonB, ref minB, ref maxB);
// Check if the polygon projections are currentlty intersecting
float intervalDistance = IntervalDistance(minA, maxA, minB, maxB);
if (intervalDistance > 0) result.IsIntersecting = false;
// ===== 2. Now find if the polygons *will* intersect =====
// Project the velocity on the current axis
float velocityProjection = axis.DotProduct(velocity);
// Get the projection of polygon A during the movement
if (velocityProjection < 0) {
minA += velocityProjection;
} else {
maxA += velocityProjection;
}
// Do the same test as above for the new projection
intervalDistance = IntervalDistance(minA, maxA, minB, maxB);
if (intervalDistance > 0) result.WillIntersect = false;
// If the polygons are not intersecting and won't intersect, exit the loop
if (!result.IsIntersecting && !result.WillIntersect) 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;
Vector d = polygonA.Center - polygonB.Center;
if (d.DotProduct(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;
}
/// <summary>
/// Test if two polygons collide by testing each line segment in polygon 1 against each line segment in polygon 2.
/// Returns a parially filled SvgCollision.PolygonCollisionResult.
/// </summary>
/// <param name="ptsA">Polygon 1 point array</param>
/// <param name="ptsB">Polygon 2 point array</param>
/// <returns></returns>
public static SvgCollision.PolygonCollisionResult PolygonCollision(PointF[] ptsA, PointF[] ptsB)
{
SvgCollision.PolygonCollisionResult result = new SvgCollision.PolygonCollisionResult();
result.LineIntersectingPoints = new List<PointF>();
PointF previousA = new PointF();
PointF previousB = new PointF();
foreach (PointF ptsa in ptsA)
{
if (!(previousA.IsEmpty))
{
foreach (PointF ptsb in ptsB)
{
if (!(previousB.IsEmpty))
{
if (ptsa != ptsb && previousA != previousB)
{
bool blurp = DoLinesIntersect(previousA, ptsa, previousB, ptsb);
if (blurp)
{
result.IsIntersecting = true;
result.OnPath = true;
PointF intersection;
LineIntersectionPoint(ptsa, previousA, ptsb, previousB, out intersection);
result.LineIntersectingPoints.Add(intersection);
}
}
}
previousB = ptsb;
}
previousB = new PointF();
}
previousA = ptsa;
}
return result;
}
