void projectPolygon(Vector axis, ConvexPolygon polygon, qreal &min, qreal &max)
{
// To project a point on an axis use the dot product
//qDebug() << "Projecting on "<< axis;
qreal d = axis.dotProduct(polygon.at(0));
min = d;
max = d;
for (int i = 0; i < polygon.size(); i++)
{
d= polygon.at(i).dotProduct (axis);
if (d < min)
min = d;
else
if (d> max) max = d;
// qDebug() << "p="<<polygon.at(i)<<" d="<<d<<" (min, max)=("<<min<<","<<max<<")";
}
}
PolygonCollisionResult polygonCollision(ConvexPolygon polygonA,
ConvexPolygon polygonB, Vector velocity)
{
PolygonCollisionResult result;
result.intersect = true;
result.willIntersect = true;
int edgeCountA = polygonA.size();
int edgeCountB = polygonB.size();
qreal minIntervalDistance = 1000000000;
QPointF translationAxis;
QPointF edge;
/*
qDebug() << "A: ";
for (int k=0; k<edgeCountA;k++)
qDebug() <<polygonA.at(k);
qDebug() << "B: ";
for (int k=0; k<edgeCountB;k++)
qDebug() <<polygonB.at(k);
qDebug() ;
*/
// Loop through all the edges of both polygons
for (int i=0;i<edgeCountA + edgeCountB;i++)
{
if (i< edgeCountA)
{
// Loop through polygon A
if (i<edgeCountA-1)
edge = QPointF (
polygonA.at(i+1).x()-polygonA.at(i).x(),
polygonA.at(i+1).y()-polygonA.at(i).y());
else
edge = QPointF (
polygonA.at(0).x()-polygonA.at(i).x(),
polygonA.at(0).y()-polygonA.at(i).y());
} else
{
// Loop through polygon B
if (i < edgeCountA +edgeCountB -1 )
edge = QPointF (
polygonB.at(i-edgeCountA+1).x() - polygonB.at(i-edgeCountA).x(),
polygonB.at(i-edgeCountA+1).y() - polygonB.at(i-edgeCountA).y());
else
edge = QPointF (
polygonB.at(0).x() - polygonB.at(i-edgeCountA).x(),
polygonB.at(0).y() - polygonB.at(i-edgeCountA).y());
}
// ===== 1. Find if the polygons are currently intersecting =====
// Find the axis perpendicular to the current edge
Vector axis (-edge.y(), edge.x());
axis.normalize();
// Find the projection of the polygon on the current axis
qreal minA = 0; qreal minB = 0; qreal maxA = 0; qreal maxB = 0;
projectPolygon(axis, polygonA, minA, maxA);
projectPolygon(axis, polygonB, minB, maxB);
// Check if the polygon projections are currentlty intersecting
qreal d = intervalDistance(minA, maxA, minB, maxB);
if (d > 0) result.intersect = false;
// ===== 2. Now find if the polygons *will* intersect =====
// Project the velocity on the current axis
qreal 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
// d = intervalDistance(minA, maxA, minB, maxB);
//if (d > 0) result.willIntersect = false;
/*
qDebug() <<" ";
qDebug() << "edge="<<edge<<" ";
qDebug() <<"axis="<<axis<<" ";
qDebug() <<"dA=("<<minA<<","<<maxA<<") dB=("<<minB<<","<<maxB<<")";
qDebug() <<" d="<<d<<" ";
//qDebug() <<"minD="<<minIntervalDistance<<" ";
qDebug() <<"int="<<result.intersect<<" ";
//qDebug() <<"wint="<<result.willIntersect<<" ";
//qDebug() <<"velProj="<<velocityProjection<<" ";
qDebug() ;
*/
if (result.intersect )// || result.willIntersect)
{
// 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
if (d<0) d=-d;
if (d < minIntervalDistance) {
minIntervalDistance = d;
//translationAxis = axis;
//qDebug() << "tAxix="<<translationAxis;
//QPointF t = polygonA.Center - polygonB.Center;
//QPointF t = polygonA.at(0) - polygonB.at(0);
//if (dotProduct(t,translationAxis) < 0)
// translationAxis = -translationAxis;
}
}
}
// The minimum translation vector
// can be used to push the polygons appart.
if (result.willIntersect)
result.minTranslation =
translationAxis * minIntervalDistance;
return result;
}
