trackball.h

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/*
 * trackball.h
 * A virtual trackball implementation
 * Written by Gavin Bell for Silicon Graphics, November 1988.
 */
 
/*
 * Pass the x and y coordinates of the last and current positions of
 * the mouse, scaled so they are from (-1.0 ... 1.0).
 *
 * The resulting rotation is returned as a quaternion rotation in the
 * first parameter.
 */
void trackball( double q[4], double p1x, double p1y, double p2x, double p2y );
 
/*
 * Given two quaternions, add them together to get a third quaternion.
 * Adding quaternions to get a compound rotation is analogous to adding
 * translations to get a compound translation.  When incrementally
 * adding rotations, the first argument here should be the new
 * rotation, the second and third the total rotation (which will be
 * over-written with the resulting new total rotation).
 */
void add_quats( double *q1, double *q2, double *dest );
 
/*
 * A useful function, builds a rotation matrix in Matrix based on
 * given quaternion.
 */
void build_rotmatrix( float m[4][4], double q[4] );
 
/*
 * This function computes a quaternion based on an axis (defined by
 * the given vector) and an angle about which to rotate.  The angle is
 * expressed in radians.  The result is put into the third argument.
 */
void axis_to_quat( double a[3], double phi, double q[4] );