// WhichPot.cpp     
// NKU CSC 480/580 - Kirby
// ------------------------------------------------------------------------------------------
// Demonstrating:
//   - Picking.
// Slightly revised 4/28/06: Replaced orthographic with perspective projection (lines 49-50).
// ------------------------------------------------------------------------------------------


#include <GL/glut.h>
#include <iostream>
using namespace std ;


bool gTopView= false ;  // front/top view: toggled by space bar.



void lighting()
// Set up some simple lighting and materials for our teapots.
{
    const float YELLOW[]={1,1,0,0}, WHITE[]={1,1,1,0}, GREY[]={0.3, 0.3, 0.3, 0 } ;
    
    // Set up the appropriate processing steps for lighting.
    glEnable( GL_DEPTH_TEST ) ;
    glPolygonMode( GL_FRONT, GL_FILL ) ;
    glEnable( GL_NORMALIZE ) ; 
    glEnable( GL_LIGHTING ) ;

    // One Phong light source    
    float lightPos[]= {1,1,1,0} ;  
    glLightfv( GL_LIGHT0, GL_POSITION, lightPos ) ;  
    glLightfv( GL_LIGHT0, GL_DIFFUSE, WHITE ) ;
    glLightfv( GL_LIGHT0, GL_AMBIENT, GREY ) ;
    glEnable( GL_LIGHT0 ) ;

    // The material for all the solids drawn will be default yellow.
    glMaterialfv( GL_FRONT, GL_DIFFUSE,  YELLOW );   
}



void drawTeapots( GLenum mode )
// Draw a scene of three teapots at three depths, overlapping from viewpoint, in given mode.
{
    // Projection (common to both rendering and selection modes)
    glMatrixMode( GL_PROJECTION ) ;
    double s= 2 ;
    gluPerspective( 30., 1., 6, 10 ) ;
    gluLookAt( 0,0,8, 0,0,0, 0,1,0 ) ;
    
    // Switch to model view for manipulation of scene
    glMatrixMode( GL_MODELVIEW ) ;
    glPushMatrix() ;
    {
        if ( gTopView )
            glRotated( 90, 1,0,0 ) ;  // "view" part of modelview
            
        // Set up lighting (subject to modelview) 
        lighting() ;
    
        // Teapot 1 (name 100) forward, top right
        glPushMatrix() ;  
            glTranslated( 0.5, 0.5 ,1.3 ) ;
            if ( mode == GL_SELECT )
                glLoadName( 100 ) ;
            glutSolidTeapot( 0.5 ) ;
        glPopMatrix() ;

        // Teapot 2 (name 200) middle, center
        glPushMatrix() ; 
            if ( mode == GL_SELECT )
                glLoadName( 200 ) ;
            glutSolidTeapot( 0.5 ) ;
        glPopMatrix() ;

        // Teapot 3 (name 300) behind, bottom left
        glPushMatrix() ; 
            glTranslated( -0.5, -0.5, -1.3 ) ;
            if ( mode == GL_SELECT )
                glLoadName( 300 ) ;
            glutSolidTeapot( 0.5 ) ;
        glPopMatrix() ;  
    }
    glPopMatrix() ;   
}



void display()  
{
    // In rendering mode, we start with identity projection.
    glMatrixMode( GL_PROJECTION ) ;
    glLoadIdentity() ;
    
    // Draw scene.
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ) ;
    drawTeapots( GL_RENDER ) ;         
    glutSwapBuffers() ;
}



void reportHits( int nHits, unsigned int nameBuffer[] )
// Print out information about hits on console.
// Reference: OpenGL Red Book p.536.
{
    cout << "This click triggered " << nHits << " hits." << endl ;
    
    unsigned int* pi= nameBuffer ;
    for ( int i=0 ; i < nHits ; ++i )
    {
        int    nNames=   (int) *pi++ ;
        float  minDepth= (float) (*pi++)/0xFFFFFFFF ; 
        float  maxDepth= (float) (*pi++)/0xFFFFFFFF ;
        
        cout << "  Hit " << (i+1) << " [depth " << minDepth << " ... " << maxDepth << "].  Names: " ;
        for ( int j=0 ; j < nNames ; ++j )
            cout << "   " << *pi++  ;
        cout << endl ;
    }
}



void pickAt( int ix, int iy, double r )
// Mouse click at (ix,iy): draw in selection mode and report hits in box 
// of size r around click location.
{
    cout << "\nClick at " << ix << ", " << iy << endl ;

    // Initialize name buffer.
    const int BUFSIZE= 512 ;
    static unsigned int nameBuffer[ BUFSIZE ] ;
    glSelectBuffer( BUFSIZE, nameBuffer ) ;
    glRenderMode( GL_SELECT ) ;
    glInitNames() ;
    glPushName( 0 ) ;
    
    // Grab viewport.
    int vport[4] ;
    glGetIntegerv( GL_VIEWPORT, vport ) ;
    int iyMax= vport[3] ;
    
    // Define special projection matrix for picking, then draw.
    glMatrixMode( GL_PROJECTION ) ;
    glPushMatrix() ;
    {
        glLoadIdentity() ; 
        gluPickMatrix( (double) ix, (double)( iyMax-iy ), r, r, vport ) ;
        drawTeapots( GL_SELECT ) ;
    }
    glMatrixMode( GL_PROJECTION ) ;
    glPopMatrix() ;
    
    // Process hits
    int nHits= glRenderMode( GL_RENDER ) ;
    reportHits( nHits, nameBuffer ) ;
    
    glutPostRedisplay() ;
    glPopName() ;
}



void mouseClick( int button, int state, int ix, int iy )
// Event handler for mouse click event.
{
    if ( button == GLUT_LEFT_BUTTON  &&  state == GLUT_DOWN )
        pickAt( ix, iy, 4 ) ;
}



void kbDispatch( unsigned char ch, int x, int y )
// Adjust view: front/top.
{
    if ( ch == ' ' )
        gTopView= ! gTopView ;
    glutPostRedisplay() ;
}



int main( int argc, char** argv )
{
    // Initialize OpenGL. 
    glutInit( &argc, argv ) ;
    glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH ) ; 

    // Window attributes.
    glutInitWindowSize( 700, 700 ) ;
    glutInitWindowPosition( 100, 100 ) ;
    glutCreateWindow( "Which Pot?" ) ;

    // Register callbacks.
    glutMouseFunc( mouseClick ) ; 
    glutKeyboardFunc( kbDispatch ) ;
    glutDisplayFunc( display ) ;  

    // Go.
    glutMainLoop() ;
  
    return 0 ;
}