android - min3D library - quaternion rotation issue -

i rendered 3d model using min3d library in application.
used quaternion data (x,y,z,w) rotation , flipping.

the rotation perfect front face , when flip opposite face rotation becomes opposite actual direction.
mean "on opposite face", when rotate right, cube rotates left , vice-versa.

the code used:

 @override public void initscene() {         light light = new light();     light.position.setallfrom(scene.camera().position);     scene.lights().add(light);     scene.backgroundcolor().setall(0xffffff);     try {         iparser parser = parser.createparser(parser.type.obj,                 getresources(), "---:raw/cube_obj", true);         parser.parse();         cube = parser.getparsedobject();         cube.scale().x = cube.scale().y = cube.scale().z = .08f;         cube.position().x = .3f;         scene.addchild(cube);         scene.camera().target = cube.position();         mdoplotting =true;     } catch (outofmemoryerror e) {         e.printstacktrace();              } 

in object3d.java

private quaternion _quaternion = new quaternion(new vector3(0.0,0.0,0.0),math.toradians(0)); public quaternion quaternion() {     return _quaternion; } 

in quaternion.java

public final class quaternion { public double x; public double y; public double z; public double w;  public quaternion(final quaternion q) {     this(q.x, q.y, q.z, q.w); }  public quaternion(double x, double y, double z, double w) {     this.x = x;     this.y = y;     this.z = z;     this.w = w; }  public void set(final quaternion q) {     this.x = q.x;     this.y = q.y;     this.z = q.z;     this.w = q.w; }  public quaternion(vector3 axis, double angle) {     set(axis, angle); }  public double norm() {     return math.sqrt(dot(this)); }  public double getw() {     return w; }  public double getx() {     return x; }  public double gety() {     return y; }  public double getz() {     return z; }   public quaternion set(vector3 axis, double angle) {     double s =  math.sin(angle / 2);     w = math.cos(angle / 2);     x = axis.getx() * s;     y = axis.gety() * s;     z = axis.getz() * s;     return this; }  public quaternion multhis(quaternion q) {     double nw = w * q.w - x * q.x - y * q.y - z * q.z;     double nx = w * q.x + x * q.w + y * q.z - z * q.y;     double ny = w * q.y + y * q.w + z * q.x - x * q.z;     z = w * q.z + z * q.w + x * q.y - y * q.x;     w = nw;     x = nx;     y = ny;     return this; }  public quaternion setrotation( vector3 v, float angle){ double s = (double) math.sin(angle / 2); w = (double) math.cos(angle / 2); x = v.x*s; y = v.y*s; z = v.z*s; return this; } public void setrotation(double x, double y, double z, double angle){     //        float half = angle*0.5f;     double s = (double) math.sin(angle / 2);     this.x = x*s;     this.y = y*s;     this.z = z*s;     w = (double) math.cos(angle / 2);  }  public void rotatethis(double x,double y,double z,double w){     this.x = x;     this.y = y;     this.z = z;     this.w = w; }  public quaternion scalethis(double scale) {     if (scale != 1) {         w *= scale;         x *= scale;         y *= scale;         z *= scale;     }     return this; }  public quaternion divthis(double scale) {     if (scale != 1) {         w /= scale;         x /= scale;         y /= scale;         z /= scale;     }     return this; }  public double dot(quaternion q) {     return x * q.x + y * q.y + z * q.z + w * q.w; }  public boolean equals(quaternion q) {     return x == q.x && y == q.y && z == q.z && w == q.w; }  public quaternion interpolatethis(quaternion q, double t) {     if (!equals(q)) {         double d = dot(q);         double qx, qy, qz, qw;          if (d < 0f) {             qx = -q.x;             qy = -q.y;             qz = -q.z;             qw = -q.w;             d = -d;         } else {             qx = q.x;             qy = q.y;             qz = q.z;             qw = q.w;         }          double f0, f1;          if ((1 - d) > 0.1f) {             double angle = (double) math.acos(d);             double s = (double) math.sin(angle);             double tangle = t * angle;             f0 = (double) math.sin(angle - tangle) / s;             f1 = (double) math.sin(tangle) / s;         } else {             f0 = 1 - t;             f1 = t;         }          x = f0 * x + f1 * qx;         y = f0 * y + f1 * qy;         z = f0 * z + f1 * qz;         w = f0 * w + f1 * qw;     }      return this; }  public quaternion normalizethis() {     return divthis(norm()); }  public quaternion interpolate(quaternion q, double t) {     return new quaternion(this).interpolatethis(q, t); }   public float[] tomatrix() {     float[] matrixs = new float[16];     tomatrix(matrixs);     return matrixs; }  public final void tomatrix(float[] matrixs) {     matrixs[3] = 0.0f;     matrixs[7] = 0.0f;     matrixs[11] = 0.0f;     matrixs[12] = 0.0f;     matrixs[13] = 0.0f;     matrixs[14] = 0.0f;     matrixs[15] = 1.0f;      matrixs[0] = (float) (1.0f - (2.0f * ((y * y) + (z * z))));     matrixs[1] = (float) (2.0f * ((x * y) - (z * w)));     matrixs[2] = (float) (2.0f * ((x * z) + (y * w)));      matrixs[4] = (float) (2.0f * ((x * y) + (z * w)));     matrixs[5] = (float) (1.0f - (2.0f * ((x * x) + (z * z))));     matrixs[6] = (float) (2.0f * ((y * z) - (x * w)));      matrixs[8] = (float) (2.0f * ((x * z) - (y * w)));     matrixs[9] = (float) (2.0f * ((y * z) + (x * w)));     matrixs[10] = (float) (1.0f - (2.0f * ((x * x) + (y * y)))); } 

}

i used

 cube.quaternion().rotatethis( event3d.getx(),event3d.gety(),event3d.getz(),event3d.getw()); 

for rotation

i not sure because of touch event (if using ontouch user rotating cube), x axis of screen take left of screen right positive. , 3d model/camera rotating positively in anti-clockwise. so, maybe reason why it's in reverse direction. confirm may code how track down user action rotating cube. sorry can't use comment.