polygon_bounds()

std::function< bool(glm::vec2)> MayaFlux::Kinesis::polygon_bounds ( std::span< const glm::vec2 >  vertices )

inline

Containment test for a convex or concave polygon.

Uses the winding number algorithm, which handles both convex and non-convex polygons correctly. Vertices are in NDC, ordered either clockwise or counter-clockwise.

Parameters

vertices

Polygon vertices. Copied into the closure.

Definition at line 227 of file Bounds.hpp.

{
    std::vector<glm::vec2> verts(vertices.begin(), vertices.end());
    return [verts = std::move(verts)](glm::vec2 p) {
        int winding = 0;
        size_t n = verts.size();
        for (size_t i = 0; i < n; ++i) {
            glm::vec2 a = verts[i];
            glm::vec2 b = verts[(i + 1) % n];
            if (a.y <= p.y) {
                if (b.y > p.y) {
                    float cross = (b.x - a.x) * (p.y - a.y)
                        - (b.y - a.y) * (p.x - a.x);
                    if (cross > 0.0F)
                        ++winding;
                }
            } else {
                if (b.y <= p.y) {
                    float cross = (b.x - a.x) * (p.y - a.y)
                        - (b.y - a.y) * (p.x - a.x);
                    if (cross < 0.0F)
                        --winding;
                }
            }
        }
        return winding != 0;
    };
}

References a, and b.

Referenced by MayaFlux::Portal::Forma::Geometry::drawable_canvas(), and MayaFlux::Portal::Forma::Geometry::position_picker().

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