/* melite1b.c - visualizza un pianeta e un satellite artificiale in 2D
 *	usando le primitive viste
 * 
 *  Autore: Andrea Fusiello, Andrea Colombari 2004
 *
 *	arrow keys		- move planet and artificial satellite coherently  
 *	s key			- commuta tra modalita' con shading e flat
 *	Escape Key		- esce dal programma
 */

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <GL/glut.h>	/* includes gl.h, glu.h */

/* Function Prototypes */

void initgfx( void );
void keyboard( GLubyte, GLint, GLint );
void specialkeys( GLint, GLint, GLint );
void drawScene( void );

void checkError( char * );
void printHelp( char * );


/* Global Definitions */

GLboolean flat = GL_TRUE;
GLdouble x;
GLdouble y;
GLdouble g_v;

#define KEY_ESC	27	/* ascii value for the escape key */

int 
main( int argc, char *argv[] )
{
	GLsizei width, height;

	glutInit( &argc, argv );

	width = glutGet( GLUT_SCREEN_WIDTH ); 
	height = glutGet( GLUT_SCREEN_HEIGHT );
    
	glutInitWindowPosition( width / 4, height / 4 );
	glutInitWindowSize( width / 2, height / 2 );
	glutInitDisplayMode( GLUT_RGBA );
	glutCreateWindow( argv[0] );

	initgfx();

	glutKeyboardFunc( keyboard );
	glutSpecialFunc( specialkeys );
	glutDisplayFunc( drawScene ); 

	printHelp( argv[0] );

	glutMainLoop();
    
    return(0);
}

void printHelp( char *progname )
{
	fprintf(stdout, 
		"\n%s - elite in 2D with moving objects\n\n"
		"arrow keys - move planet and artificial satellite coherently\n"
		"<s> key    - toggle smooth/flat shading\n"
		"Escape Key - exit the program\n\n",
		progname);
}

void initgfx( void )
{
	/* set clear color to black */
	glClearColor( 0.0, 0.0, 0.0, 1.0 );
	glOrtho( -4.0f, 4.0f, -3.0f, 3.0f, -3.0f, 3.0f );
    y = 0;
    x = 0;
    g_v = 0.2;    
}

void checkError( char *label )
{
	GLenum error;
	while ( (error = glGetError()) != GL_NO_ERROR )
		printf( "%s: %s\n", label, gluErrorString(error) );
}

void keyboard( GLubyte key, GLint x, GLint y )
{   
	switch (key) {
	case 's':	/* s key */
		if (flat)
			glShadeModel( GL_FLAT );
		else 
			glShadeModel( GL_SMOOTH );
		glutPostRedisplay();

		/* toggle between smooth and flat shading */
		flat = !flat;
		break;
	case KEY_ESC:	/* Exit when the Escape key is pressed */
		exit(0);
	}
}

void specialkeys( GLint key, GLint u, GLint v )
{   
	/* arrow keys */
		/* move the point of view */
	switch (key) {
	case GLUT_KEY_UP:
        y += g_v;
		glutPostRedisplay();
		break;
	case GLUT_KEY_DOWN:
        y -= g_v;
		glutPostRedisplay();
		break;
	case GLUT_KEY_LEFT:
        x -= g_v;
		glutPostRedisplay();
		break;
	case GLUT_KEY_RIGHT:
        x += g_v;
		glutPostRedisplay();
		break;
	}
}

void drawScene( void )
{
	static GLfloat yellow[] = { 1.0f, 1.0f, 0.0f };
	static GLfloat darkgreen[] = { 0.0f, 0.25f, 0.0f };
	static GLfloat blue[] = { 0.0f, 0.0f, 1.0f };
	static GLfloat grey[] = { 0.5f, 0.5f, 0.5f };

	glClear( GL_COLOR_BUFFER_BIT );
	//glOrtho( -4.0f, 4.0f, -3.0f, 3.0f, -3.0f, 3.0f );

	/* Do all your OpenGL rendering here */
   
	/* Draw a triangle fan for the planet; make
	 * the center yellow, and the edges darkgreen
	 */
	glBegin( GL_TRIANGLE_FAN );
	  glColor3fv( yellow );
	  glVertex2f( x, y );
	  glColor3fv( darkgreen );
	  glVertex2f( x, y-1.5f );
	  glVertex2f( x+1.5f, y-0.8f );
	  glVertex2f( x+1.5f, y+0.8f );
	  glVertex2f( x, y+1.5f );
	  glVertex2f( x-1.5f, y+0.8f );
	  glVertex2f( x-1.5f, y-0.8f );
	  glVertex2f( x, y-1.5f );
	glEnd();    
	
	/* Draw a triangle strip for the spaceship;
	 * use your fantasy to give it a shape
	 * and use two different color (e.g. blue and 
	 * grey) for shading */
	glBegin( GL_TRIANGLE_FAN );
	  glColor3fv( blue );
	  glVertex2f( x+2.1f, y+2.0f );
	  glColor3fv( grey );
	  glVertex2f( x+2.2f, y+2.2f );
	  glVertex2f( x+1.8f, y+2.0f );
	  glVertex2f( x+2.2f, y+1.8f );
	  glVertex2f( x+2.1f, y+2.0f );
	glEnd();    

	checkError( "drawScene" );
	glFlush();
}