// single point rotation
rotate :: (p: *Vec2s64, center: Vec2s64, angle: s64) {
    rad := cast(float64)angle * (PI / 180.0);

    // translate to center
    tx := p.x - center.x;
    ty := p.y - center.y;

    // apply rotation
    rx := cast(s64)(tx * cos(rad) - ty * sin(rad));
    ry := cast(s64)(tx * sin(rad) + ty * cos(rad));

    // translate back
    p.x = rx + center.x;
    p.y = ry + center.y;
}

// rotate n points
rotate :: (pn: ..*Vec2s64, center: Vec2s64, angle: s64) {
    for pn {
        rotate(it, center, angle);
    }
}

// rotate 3 points via triangle struct
rotate :: (t: *Triangle, center: Vec2s64, angle: s64) {
    rotate(*t.p1, *t.p2, *t.p3, center = center, angle = angle);
}

// rotate 4 points via quad struct
rotate :: (q: *Quad, center: Vec2s64, angle: s64) {
    rotate(*q.p1, *q.p2, *q.p3, *q.p4, center = center, angle = angle);
}