円と線分の交点算出

HItCheck

// A,Bは線分、Cは円の中心
auto PointA = Vector2();
auto PointB = Vector2();
auto PointC = Vector2();

auto VecAtoB = Vector2( PointB - PointA );
auto VecAtoC = Vector2( PointC - PointA );
auto VecBtoC = Vector2( PointC - PointB );

// 角度の算出
auto N = VecAtoB.x * VecAtoC.y - VecAtoB.y * VecAtoC.x;
auto D = VecAtoB.x * VecAtoC.x + VecAtoB.y * VecAtoC.y;
auto Theta = atan2(N,D);

// 交点座標の算出
auto Length = abs( VecAtoC.length * sin( Theta ) );