/* demoDisplayList.c : */

/* 
	Purpose: construct a box and the letter O using Display lists.
*/


#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#define KEY_ESC 27      /* glut doesn't define this one  */
#define PI 3.14159265

GLuint BOX;
GLuint OSHAPE; 

void printHelp( void )
{
	fprintf(stdout,
			"Display List Demo\n\n"
			"Escape key    - exit the program\n\n");
}

GLvoid keyboard( GLubyte key, GLint x, GLint y)
{
	switch (key) 
	{
	case KEY_ESC:   /* exit when escape key is pressed */
		exit(0);
	break;
    }
}

GLvoid specialkeys( GLint key, GLint x, GLint y)
{
    switch (key) 
	{
    case GLUT_KEY_F1:   /* print Help information */
         printHelp();
         break;
    }
}

GLvoid checkError( const char* const label )
{
	GLenum error;

	error = glGetError();
	while ( GL_NO_ERROR != error )
	{
		fprintf( stderr,"%s: %s\n", label, gluErrorString(error) );
		error = glGetError();
	}
}

void reshape(GLint width, GLint height)
{
	GLdouble aspect;
	aspect = (GLdouble)width / (GLdouble)height;
	/* update the viewport */
	glViewport(0,0,width,height);
	/* reset viewing volume */
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	/* match VV with aspect ratio of Viewport */
	if (width > height)
	{
		glOrtho(-4*aspect, 4*aspect, -4, 4, -2, 2);
	}
	else
	{
		glOrtho(-4, 4, -4/aspect, 4/aspect, -2, 2);
	}
	glMatrixMode(GL_MODELVIEW);
}

GLvoid createBoxList( GLvoid )
{
	BOX = glGenLists(1);
	glNewList(BOX, GL_COMPILE);
		glBegin( GL_POLYGON );
			glColor3f(1.0,0.0,0.0);
			glVertex2f(-1.0,-1.0);
			glVertex2f(1.0,-1.0);
			glVertex2f(1.0,1.0);
			glVertex2f(-1.0,1.0);
		glEnd();
	glEndList();
}

GLvoid createOshapeList( GLvoid )
{
	OSHAPE = glGenLists(1);
	glNewList(OSHAPE, GL_COMPILE);
	{
		float angle;
		int i;
		glBegin( GL_QUAD_STRIP );
			for (i=0; i<=12; i++)  /* 12 vertices around our letter O  */
			{
				angle = PI / 6.0 * i;  /* 30 degrees in radians  */
				glVertex2f(0.4*cos(angle), 0.4*sin(angle) );
				glVertex2f(0.5*cos(angle), 0.5*sin(angle) );
			}
		glEnd();
	}
	glEndList();
}

GLvoid display( GLvoid )
{

	/* Do all your OpenGL rendering here */

	glClear( GL_COLOR_BUFFER_BIT );   

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	glCallList(BOX);
	glCallList(OSHAPE);

/* To display another O-shape, larger and to one side:  */

	glTranslatef(2.0,0.0,0.0);   
	glScalef(2.0,2.0,1.0);

	glCallList(OSHAPE);

	checkError( "display" );
	glFlush();
}

void init( void )
{
	glClearColor( 1.0, 1.0, 1.0, 1.0);
	glPolygonMode(GL_FRONT,GL_LINE);

	createBoxList();
	createOshapeList();
}


int main( int argc, char *argv[] )
{
	
	glutInit( &argc, argv );

	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );  

	glutCreateWindow( argv[0] );
	printHelp();

	glutDisplayFunc( display );
	glutReshapeFunc( reshape );

    glutKeyboardFunc( keyboard );
    glutSpecialFunc( specialkeys );

	init();

	glutMainLoop();

	return 0;
}