#          light
#
#  This program demonstrates the use of the OpenGL lighting model.  
#  A icosahedron is drawn using a grey material characteristic. 
#  A single light source illuminates the object.
#  Example adapted from light.c.
use OpenGL;
$use_lighting=1;
$use_frame=1;
sub icosahedron{
    # from OpenGL Programming Guide page 56
    $x=0.525731112119133606;
    $z=0.850650808352039932;
    $v=[
        [-$x,   0,  $z],
        [ $x,   0,  $z],
        [-$x,   0, -$z],
        [ $x,   0, -$z],
        [  0,  $z,  $x],
        [  0,  $z, -$x],
        [  0, -$z,  $x],
        [  0, -$z, -$x],
        [ $z,  $x,   0],
        [-$z,  $x,   0],
        [ $z, -$x,   0],
        [-$z, -$x,   0],
       ];
    $t=[
        [0,4,1],        [0, 9, 4],
        [9, 5, 4],      [4, 5, 8],
        [4, 8, 1],      [8, 10, 1],
        [8, 3, 10],     [5, 3, 8],
        [5, 2, 3],      [2, 7, 3],
        [7, 10, 3],     [7, 6, 10],
        [7, 11, 6],     [11, 0, 6],
        [0, 1, 6],      [6, 1, 10],
        [9, 0, 11],     [9, 11, 2],
        [9, 2, 5],      [7, 2, 11],
       ];
    for($i=0;$i<20;$i++) {
        glBegin(GL_POLYGON);
            for($j=0;$j<3;$j++) {
                $use_lighting || glColor3f(0,$i/19.0,$j/2.0);
                glNormal3f( $v->[$t->[$i][$j]][0],
                                $v->[$t->[$i][$j]][1],
                                $v->[$t->[$i][$j]][2]);
                glVertex3f( $v->[$t->[$i][$j]][0],
                                $v->[$t->[$i][$j]][1],
                                $v->[$t->[$i][$j]][2]);
            }
        glEnd();
        if( $use_frame){
            glPushAttrib(GL_ALL_ATTRIB_BITS);
            glDisable(GL_LIGHTING);
            glColor3f(1,0,0);
            glBegin(GL_LINE_LOOP);
                for($j=0;$j<3;$j++) {
                glVertex3f(     1.01 * $v->[$t->[$i][$j]][0],
                                1.01 * $v->[$t->[$i][$j]][1],
                                1.01 * $v->[$t->[$i][$j]][2]);
                }
            glEnd();
            glPopAttrib();
        }
    }
}
sub myinit{
    # Initialize material property, light source, lighting model, 
    # and depth buffer.
    @mat_specular = ( 1.0, 1.0, 0.0, 1.0 );
    @mat_diffuse  = ( 0.0, 1.0, 1.0, 1.0 );
    @light_position = ( 1.0, 1.0, 1.0, 0.0 );
    glMaterialfv(GL_FRONT, GL_DIFFUSE, pack("f4",@mat_diffuse));
    glMaterialfv(GL_FRONT, GL_SPECULAR, pack("f4",@mat_specular));
    glMaterialf(GL_FRONT, GL_SHININESS, 10);
    glLightfv(GL_LIGHT0, GL_POSITION, pack("f4",@light_position));
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glDepthFunc(GL_LESS);
    glEnable(GL_DEPTH_TEST);
} 
sub display {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();
    glRotatef(23*sin($spin*3.14/180),1,0,0);
    glRotatef($spin,0,1,0);
    icosahedron;
    glPopMatrix();
    glFlush();
    glXSwapBuffers();
}
sub myReshape {
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-1.5, 1.5, -1.5, 1.5, -10.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
  
glpOpenWindow(width=>300,height=>300,
        attributes=> [GLX_DOUBLEBUFFER,GLX_RGBA,
                GLX_DEPTH_SIZE,16,
                GLX_RED_SIZE,1,
                GLX_GREEN_SIZE,1,
                GLX_BLUE_SIZE,1]);
$use_lighting && myinit();
myReshape();
glEnable(GL_DEPTH_TEST);
glRotatef(0.12,1,0,0);
while(1){$spin+=1;display;}