Find Rotation Axis

        //This part of code should be in the else block of mouseMoveEvent() function of glMain.cpp
        const int dx = x - _mouseX;
        const int dy = y - _mouseY;
        
        int fviewport[]={0,0,1,1};
        double projection[16];
        double modelview[16];
        
        glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
        glGetDoublev( GL_PROJECTION_MATRIX, projection );
        
        double bl[3];
        double br[3];
        double tl[3];
        
        gluUnProject(0, 0, 0, modelview, projection, fviewport, &bl[0], &bl[1], &bl[2]);
        gluUnProject(1, 0, 0, modelview, projection, fviewport, &br[0], &br[1], &br[2]);
        gluUnProject(0, 1, 0, modelview, projection, fviewport, &tl[0], &tl[1], &tl[2]);
        
        double v1[]={br[0]-bl[0], br[1]-bl[1], br[2]-bl[2]};
        double v2[]={tl[0]-bl[0], tl[1]-bl[1], tl[2]-bl[2]};
        
        double cr[]={v1[1]*v2[2]-v1[2]*v2[1], v1[2]*v2[0]-v1[0]*v2[2], v1[0]*v2[1]-v1[1]*v2[0]};
        double norm=sqrt(cr[0]*cr[0]+cr[1]*cr[1]+cr[2]*cr[2]);//rotation axis
        
        
        cr[0]/=norm;cr[1]/=norm;cr[2]/=norm;
        
        float q[4];
        float v[]={(float)cr[0], (float)cr[1], (float)cr[2]};
        
        axistoQuat(v, -dx/100.0, q);        //Rotation axis to quaternion
        
        //You can use quatToMat function provided in simpleMath library to translate quaternion to Matrix
        
        
        //Here you can add your code to apply rotation to joint. 
        
        
        
        //Update mouse position
        _mouseX = x;
        _mouseY = y;