// Checks intersection between a polygon an moving circle at inBegin + t * inDelta with radius^2 = inA * t^2 + inB * t + inC, t in [0, 1]
// Returns true when it does and returns the intersection position in outPoint and the intersection fraction (value for t) in outFraction
bool SweptCircleEdgeVertexIntersect(const Vector2 *inVertices, int inNumVertices, const Vector2 &inBegin, const Vector2 &inDelta, float inA, float inB, float inC, Vector2 &outPoint, float &outFraction)
{
// Loop through edges
float upper_bound = 1.0f;
bool collision = false;
for (const Vector2 *v1 = inVertices, *v2 = inVertices + inNumVertices - 1; v1 < inVertices + inNumVertices; v2 = v1, ++v1)
{
float t;
// Check if circle hits the vertex
Vector2 bv1 = *v1 - inBegin;
float a1 = inA - inDelta.GetLengthSquared();
float b1 = inB + 2.0f * inDelta.Dot(bv1);
float c1 = inC - bv1.GetLengthSquared();
if (FindLowestRootInInterval(a1, b1, c1, upper_bound, t))
{
// We have a collision
collision = true;
upper_bound = t;
outPoint = *v1;
}
// Check if circle hits the edge
Vector2 v1v2 = *v2 - *v1;
float v1v2_dot_delta = v1v2.Dot(inDelta);
float v1v2_dot_bv1 = v1v2.Dot(bv1);
float v1v2_len_sq = v1v2.GetLengthSquared();
float a2 = v1v2_len_sq * a1 + v1v2_dot_delta * v1v2_dot_delta;
float b2 = v1v2_len_sq * b1 - 2.0f * v1v2_dot_bv1 * v1v2_dot_delta;
float c2 = v1v2_len_sq * c1 + v1v2_dot_bv1 * v1v2_dot_bv1;
if (FindLowestRootInInterval(a2, b2, c2, upper_bound, t))
{
// Check if the intersection point is on the edge
float f = t * v1v2_dot_delta - v1v2_dot_bv1;
if (f >= 0.0f && f <= v1v2_len_sq)
{
// We have a collision
collision = true;
upper_bound = t;
outPoint = *v1 + v1v2 * (f / v1v2_len_sq);
}
}
}
// Check if we had a collision
if (!collision)
return false;
outFraction = upper_bound;
return true;
}
