polygon-intersect

// Polygon with hole
polygon(
    points=[
        [-2.5,-2.5],
        [2.5,-2.5],
        [2.5,2.5],
        [-2.5,2.5],
        [-5,-5],
        [5,-5],
        [5,5],
        [-5,5]],
    paths=[
        [0,1,2,3],
        [7,6,5,4]
    ]);

// Two Polygons
translate([0,12,0]) polygon(
    points=[
        [5.5,-2.5],
        [10.5,-2.5],
        [10.5,2.5],
        [5.5,2.5],
        [-5,-5],
        [5,-5],
        [5,5],
        [-5,5]],
    paths=[
        [0,1,2,3],
        [4,5,6,7]
    ]);

// Overlapping Polygons
translate([0,24,0]) polygon(
    points=[
        [2.5,-2.5],
        [7.5,-2.5],
        [7.5,2.5],
        [2.5,2.5],
        [-5,-5],
        [5,-5],
        [5,5],
        [-5,5]],
    paths=[
        [0,1,2,3],
        [4,5,6,7]
    ]);