TAPsOpenGLTrackball.cpp

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/******************************************************************************
TAPsOpenGLTrackball.cpp

An object using OpenGL for Trackball Rotation.

SUKITTI PUNAK   (10/06/2004)
UPDATE          (10/06/2004)
--------------------------------------------------------------------------------
Example of Usage:   See TAPsOpenGLTrackball.hpp
-----------------
******************************************************************************/
#include "TAPsOpenGLTrackball.hpp"
// Using Inclusion Model (i.e. definitions are included in declarations)
//                       (this name.cpp is included in name.hpp)
// Each friend is defined directly inside its declaration.

BEGIN_NAMESPACE_TAPs
//=============================================================================
//-----------------------------------------------------------------------------
OpenGLTrackball::OpenGLTrackball()
{
    #ifdef  TAPs_ENABLE_DEBUG
    std::cout << "Delete A OpenGLTrackball" << std::endl;
    #endif//TAPs_DEBUG_MODE

    int i;
    // initialize matrices
    for ( i = 1; i < 15; i++ )      M[i]  = Om[i] = m[i]  = 0;
    for ( i = 0; i < 16; i += 5 )   M[i]  = Om[i] = m[i] = 1;
    // initialize data members
    for ( i = 0; i < 3; i++ )       lastPos[i] = 0;
}
//-----------------------------------------------------------------------------
OpenGLTrackball::~OpenGLTrackball()
{
    #ifdef  TAPs_ENABLE_DEBUG
    std::cout << "Delete A OpenGLTrackball" << std::endl;
    #endif//TAPs_DEBUG_MODE
}
//-----------------------------------------------------------------------------
void OpenGLTrackball::MoveObject(int x, int y, int w_pix, int h_pix)
{
    int i, j, k;
    double curPos[3], dx, dy, dz;

    Trackball_ptov(x, y, w_pix, h_pix, curPos);
    dx = curPos[0] - lastPos[0];
    dy = curPos[1] - lastPos[1];
    dz = curPos[2] - lastPos[2];
    
    if (dx || dy || dz) {
        rotationAngle = 90.0 * asin(sqrt(dx*dx + dy*dy + dz*dz));
        // for small motions by angle theta
        //   (and we measure often so motions are small)
        //   sin (theta) is approximately equal to theta
        
        // axis = Pold x P
        rotationAxis[0] = lastPos[1]*curPos[2] - lastPos[2]*curPos[1];
        rotationAxis[1] = lastPos[2]*curPos[0] - lastPos[0]*curPos[2];
        rotationAxis[2] = lastPos[0]*curPos[1] - lastPos[1]*curPos[0];

        lastPos[0] = curPos[0];
        lastPos[1] = curPos[1];
        lastPos[2] = curPos[2];

        // find matrix
        glPushMatrix();
        glLoadIdentity();
        glRotated(rotationAngle, rotationAxis[0], rotationAxis[1], rotationAxis[2]);
        glGetDoublev(GL_MODELVIEW_MATRIX, m);
        glPopMatrix();

        // calculate the new matrix
        for ( i = 0; i < 4; i++ ) {
            for ( j = 0; j < 4; j++ ) {
                M[i+j*4] = 0;
                for ( k = 0; k < 4; k++ ) {
                    M[i+j*4] += m[i+k*4]*Om[k+j*4];
                }
            }
        }

        for ( i = 0; i < 16; i++ ) {
            m[i]  = M[i];
            Om[i] = M[i];
        }
    }
}
//-----------------------------------------------------------------------------
void OpenGLTrackball::StartMotion(int x, int y, int w_pix, int h_pix)
{
    startX = x; startY = y;
    curx = x; cury = y;
    Trackball_ptov(x, y, w_pix, h_pix, lastPos);
}
//-----------------------------------------------------------------------------
void OpenGLTrackball::Trackball_ptov(int x, int y, int w_pix, int h_pix, double v[3])
{
    double d, a, dx, dy;

    dx = x;
    dy = y;

    // project x,y onto a hemi-sphere centered within width and height
    v[0] =  (1.0*dx - w_pix) / w_pix;
    v[1] = -(1.0*dy - h_pix) / h_pix;


    d = v[0]*v[0] + v[1]*v[1];
    d = (d < 1.0) ? d : 1.0;    // keep below or equal to 1
    v[2] = sqrt(1-d);
    a = sqrt(d + v[2]*v[2]);
    v[0] /= a;
    v[1] /= a;
    v[2] /= a;
}
//-----------------------------------------------------------------------------
void OpenGLTrackball::Reset()
{
    int i;
    for ( i = 0; i < 16; i++ ) {
        if ( i%5 ) {
            m[i] = Om[i] = 0;
        }
        else {
            m[i] = Om[i] = 1;
        }
    }
}
//=============================================================================
END_NAMESPACE_TAPs
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