Area of rectangle-rectangle intersection

Question

Below are 2 rectangles. Given the coordinates of the rectangle vertices - (x1, y1)...(x8, y8), how can the area of the overlapping region (white in the figure below

Answer 1

If you happen to use Qt then the intersection can be computed as QPolygonF intersection. Roughly as so:

QPolygonF p1,p2, intersected;
p1 << QPointF(r1x1,r1y1) << ... << QPointF(r1x4, r1y4);
p2 << QPointF(r2x1,r2y2) << ... << QPointF(r2x4, r2y4);
intersected = p1.intersected(p2);

float area = polyArea(intersected); // see code block below

(r1 = rectangle 1, r2 = rectangle 2, with 4 respective x and y coordinates).

Now compute the area (using the already mentioned Shoelace formula):

inline float polyArea(const QPolygonF& p)
{
    //https://en.wikipedia.org/wiki/Polygon#Area_and_centroid
    const int n = p.size();
    float area = 0.0;
    for (int i=0; i

My code here: public domain