[Plib-users] R: Selecting ssEntity with mouse

[Paolo L. <p.l...@ci...>]

Johannes,
 
here is what I do:
 
float z2, x3, y3, z3;

if ( Project2d3d ( x, y, z2, x3, y3, z3 ) ) {

    sgVec3 pick_pnt = {x3, y3, z3};

    ulSetError( UL_DEBUG, "picking point (%f,%f,%f)", x3, y3, z3 );

    sgMat4 mview_mat;

    extern void get_eye_matrices( int eye, sgMat4 proj_mat, sgMat4 mview_mat
);

    get_eye_matrices( 0, NULL, mview_mat );    // my way of doing
glGetDoublev(GL_MODELVIEW_MATRIX, mview_mat)

    ssgEntityBinding *ebind = getPickedLeaf( z2, pick_pnt, mview_mat, scene
);

}

 

x, y are mouse coord, e.g. those arguments of the mouse button press GLUT
callback.

Project2d3d maps 2D's x,y to 3D's x3,y3,z3, and is listed below (borrowed
from a past post):

 

// Project2d3d is the function which will transform 2d into 3d coordinates:

int Project2d3d ( int x2, int y2, float& z2, float& x3, float& y3, float& z3
)

{

    GLint viewport[4] ;

    GLdouble modvmatrix[16], projmatrix[16] ;

    glGetIntegerv ( GL_VIEWPORT, viewport ) ;

    /* OpenGL y starts at lower left, X/Windows y starts at top left */

    GLdouble y2gl = viewport[3] - y2 ;

    /* Use GL power to find the depth of the projection */

    glReadPixels ( x2, y2gl, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &z2 ) ;

    if ( z2 >= 1 ) return 0;

    /* Some more GL magic. Get the projection and modelview matrices */

    glGetDoublev ( GL_MODELVIEW_MATRIX, modvmatrix ) ;

    glGetDoublev ( GL_PROJECTION_MATRIX, projmatrix ) ;

    GLdouble dx, dy, dz ;

    /* convert screen coords to object coords. */

    int retcode = gluUnProject ( x2, y2gl, z2, modvmatrix, projmatrix,
viewport, &dx, &dy, &dz ) ;

    x3 = dx ;

    y3 = dy ;

    z3 = dz ;

    return retcode;

}

 

getPickedLeaf actually intersects a screen-inward ray with the scene graph
content, and return the outmost leaf along the SSG coord system's z-axis.

 

ssgEntityBinding *getPickedLeaf( float zmin, sgVec3 center, sgMat4
inv_cam_mat, ssgBranch *scene )

{

    sgVec3 test_vec, cam_center, up = {0,0,1};

    sgMat4 cam_mat, _OpenGL2ssg;

    extern sgMat4 _ssgOpenGLAxisSwapMatrix; // defined in ssg.cxx

    // back to SSG coordinate system

    sgTransposeNegateMat4( _OpenGL2ssg, _ssgOpenGLAxisSwapMatrix );

    sgPostMultMat4( inv_cam_mat, _OpenGL2ssg );

    sgTransposeNegateMat4( cam_mat, inv_cam_mat );

    // rotate the world so to put the 'center' point at the center of the
scene

    sgCopyVec3( cam_center, cam_mat[3] );

    sgMakeLookAtMat4( cam_mat, cam_center, center, up );

    sgTransposeNegateMat4( inv_cam_mat, cam_mat );

    sgSetVec3( test_vec, 0, 1, 0 );

    static ssgLeaf *leaf; // its pointer goes outside

    ssgHit *results, *hit;

    int num_hits = ssgLOS ( scene, test_vec, inv_cam_mat, &results ) ;

    if ( num_hits > 0 ) {

        ulSetError( UL_DEBUG, "hits %d", num_hits );

        float min_dst; bool done = false; leaf = NULL;

        for ( int i = 0 ; i < num_hits ; i++ ) {

            ssgHit *h = &results [ i ] ;

            float dst = - h->plane[3] / h->plane[1];

            ulSetError( UL_DEBUG, "\tdst %f, zmin %f, min_dst %f", dst,
zmin, min_dst );

            if ( dst > 0 && (!done || dst < min_dst) ) {

                done = true;

                min_dst = dst;

                leaf = h->leaf;

                hit = h;

                ulSetError( UL_DEBUG, "\t\thit %d, leaf '%s', min_dst %f",
hit, leaf->getName(), min_dst );

            }

        }

        // normally at this point one could return the ssgLeaf * 'leaf', yet
I need the path-to-node string so I fill & return a ssgEntityBinding 

        if ( leaf != NULL ) {

            static ssgEntityBinding ebind;

            static char path_string[1023], *name;

            strcpy( path_string, "" );

            hit->addPath( leaf ); // doesn't include the hit leaf itself,
but we need it

            for ( int i = 0; i < hit->getNumPathEntries(); i++ ) {

                strcat( path_string, "/" );

                strcat( path_string, (name=hit->getPathEntry(i)->getName())
? name : "" );

            }

            ebind.entity = (ssgEntity**)&leaf;

            ebind.nameOrPath = ulStrDup( path_string );

            return &ebind;

        }

    }

    return NULL;

}

 

I hope the code would get compiled with little effort and finally will work.

Greetings,

Paolo Leoncini

 
 
  _____  

Da: Johannes Strömberg [mailto:joh...@gm...] 
Inviato: venerdì 23 luglio 2010 10.34
A: pli...@li...
Oggetto: [Plib-users] Selecting ssEntity with mouse



Hello, 

I need a way of selecting an object on screen using the mouse. 

How do I convert mouse input to something that I can use with my scene and
how do I find what is under the mouse?

/Johannes