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MdtBclLimit.h

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#ifndef _MDTBCLLIMIT_H
#define _MDTBCLLIMIT_H
/*
  Copyright MathEngine 2000

  $Name: t-release-0-0-5-msvcrt $

  $Id: MdtBclLimit.h,v 1.3 2000/06/27 17:15:00 gilesc Exp $
*/

/** @file
 * Constraint library limits.
 *
 * This implements hard and soft limits for the remaining degrees of freedom
 * of constraints.  All angles are specified in radians.
 */

/**
 * MdtBcl Single Limit structure.
 *
 * Specifies behaviour of the constraint at a specific individual limit
 * (either an upper or lower limit) of a motion which is otherwise
 * unconstrained by the joint's hard constraints.
 */
typedef struct
{
    /**
     * Minimum (for lower limit) or maximum (for upper limit) linear or
     * angular separation of the attached bodies, projected onto the
     * relevant axis.
     *
     * For a soft limit, the stop is a boundary rather than an absolute
     * limit.
     */
    MeReal stop;

    /**
     * The spring constant (kp) used for restitution force when a limited
     * joint reaches one of its stops.
     *
     * This limit property must be zero or positive: the default value is
     * MEINFINITY.  If the stiffness and damping of an individual limit are
     * both zero, it is effectively deactivated.
     */
    MeReal stiffness;

    /**
     * The damping term (kd) for this limit.
     *
     * This must not be negative: the default value is zero.  This property
     * is used only if the limit hardness is less than or equal to the
     * damping threshold.  If the hardness and damping of an individual
     * limit are both zero, it is effectively deactivated.
     */
    MeReal damping;

    /**
     * The ratio of rebound velocity to impact velocity
     * when the joint reaches the low or high stop.
     *
     * This is used only if the limit hardness exceeds the damping
     * threshold.  Restitution must be in the range zero to one inclusive:
     * the default value is one.
     */
    MeReal restitution;
}
MdtBclSingleLimit;

/**
 * MdtBcl Limit structure.
 *
 * Specifies behaviour of the constraint for a motion which is otherwise
 * unconstrained by the joint's hard constraints.  This motion may be
 * constrained at either an upper limit or a lower limit, or both, or
 * actuated (powered) by a force-limited motor between such limits or in the
 * absence of limits.
 */
typedef struct
{
    /**
     * Set if the corresponding degree of freedom of the joint is limited.
     *
     * Cleared (set 0) if the degree of freedom is not limited.
     */
    int limited;

    /**
     * Non-zero if the joint has overshot a limit and is
     * relaxing back to that limit, zero if bouncing.
     */
    int bRelaxingToLimit;

    /**
     * The overshoot distance.
     *
     * This is set to zero between the limits; otherwise it is the amount by
     * which the joint has overshot its limit.  This is positive beyond the
     * upper limit, negative beyond the lower.
     */
    MeReal overshoot;

    /**
     * Relative position of the attached bodies, projected onto the
     * relevant axis.
     */
    MeReal position;

    /**
     * Relative linear or angular velocity of the attached
     * bodies, projected onto the relevant axis.
     */
    MeReal velocity;

    /**
     * The limit hardness threshold.
     *
     * This value depends on the timestep and is recalculated in each
     * timestep in which a limit is exceeded.  When a limit hardness exceeds
     * this value, damping is ignored and only the restitution property is
     * used.  When the limit hardness is at or below this threshold,
     * restitution is ignored, and the hardness and damping terms are used
     * to simulate a damped spring.
     */
    MeReal damping_thresh;

    /**
     * The specific properties of the lower and upper limits.
     */
    MdtBclSingleLimit limit[2];

    /*
      Power.
    */

    /**
     * 0 for non-powered joint, -1 for powered joint
     */
    int powered;

    /**
     * Powered joint, desired velocity.
     *
     * A lower limiting velocity may be achieved if the attached bodies are
     * subject to velocity or angular velocity damping.
     */
    MeReal desired_vel;

    /**
     * Powered joint, maximum force that should be 
     * applied to reach the desired velocity.
     */
    MeReal fmax;
}
MdtBclLimit;

#endif

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