Path Constraints

Constrains a dynamic body to a built path in world space or relative to another body.

A PathConstraint keeps Body B on the curve owned by Body A. jolt_path_world() uses Jolt's fixed world as Body A; the body's initial constraint fraction is selected from the closest point on the path.

World-space path#

var cart = jolt_box_create_dynamic(-12, 0, 2, 1, 1, 1, { mass: 2 });
var rail = jolt_path_world(cart, track, {
    rotation_mode: JOLT_PATH_ROTATION_FOLLOW,
    friction_force: 8
});

Body-relative path#

var rail = jolt_path(moving_base, cart, track, {
    collision: false,
    rotation_mode: JOLT_PATH_ROTATION_FREE
});

Both bodies must be different, live managed bodies in the default world. The path is interpreted in Body A's local frame and moves with it.

Options#

Rotation modes#

Runtime state#

rail.get_fraction()
rail.get_path_distance()
rail.get_speed()
rail.get_direction()
rail.get_impulse()
rail.get_rotation_mode()
rail.get_friction_force()

get_speed() reports the relative velocity of the attached points projected onto the world-space path tangent. get_direction() returns that tangent.

Runtime friction#

if (!rail.set_friction_force(20)) {
    show_debug_message(jolt_get_error_message());
}
var friction = rail.get_friction_force();

set_friction_force(force) accepts a finite nonnegative force limit along the path and returns boolean success. Zero removes this friction. This is PathConstraint resistance, not a body's material coefficient. get_friction_force() can return zero both for a valid zero setting and on error, so check the error channel when necessary.

Verified operation contracts#

These contracts distinguish units, return values, errors and lifetime according to the current implementation. Check results: false, 0 and undefined can mean different things for different methods.