This function returns true if the given ray intersects the XY plane centered at the origin of the world coordinates. It returns a PVector object contaning the coordinates of the interesection between the ray and the plane. The ray can be automatically computed from the screen coordinates:
void draw() {
// ...
PVector p = intersectsPlane(mouseX, mouseY);
// ...
}
A ray with arbitrary origin and direction can also be provided:
void draw() {
PVector origin = new PVector(0, 0, 0);
PVector direction = new PVector(0, 0, 1);
PVector p = intersectsPlane(origin, direction);
// ...
}