/* prac3a.c   */

/* 
	Purpose: This program practises triangle fans, independent quadrilaterals and 
	quadrilateral strips, with colours and shading techniques.
*/

#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  */

/* Global Definitions */
static float v0[2] = {0.0,0.0};
static float v1[2] = {0.5,0.0};
static float v2[2] = {0.5,1.0};
static float v3[2] = {0.0,1.0};
static float v4[2] = {-0.25,1.0};
static float v5[2] = {-0.5,0.75};
static float v6[2] = {-1.0,0.0};

void printHelp( void )
{
	fprintf(stdout,
		"Triangle fans etc.\n\n"
                "SPACE key     - alternate between flat and smooth shading\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;

    case ' ':   
	{
		/* toggle between smooth and flat shading */
		static GLboolean flat = GL_FALSE;
		flat = !flat;
		flat ? glShadeModel(GL_FLAT) : glShadeModel(GL_SMOOTH);
	}
	break;
    }
	glutPostRedisplay();
}

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();
	}
}

GLvoid display( GLvoid )
{
	/* Do all your OpenGL rendering here */

	glClear( GL_COLOR_BUFFER_BIT );

	/* First draw a triangle fan, assigning colours as you wish */
	glBegin(GL_TRIANGLE_FAN);
	  glColor3f(1.0,0.25,0.25);
	  glVertex2fv(v0);
	  glColor3f(0.5,0.5,0.0);
	  glVertex2fv(v1);
	  glColor3f(1.0,0.0,0.0);
	  glVertex2fv(v2);

	  glColor3f(1.0,1.0,0.0);
	  glVertex2fv(v3);
	  glColor3f(0.0,1.0,0.0);
	  glVertex2fv(v4);
	  glColor3f(0.0,0.5,0.5);
	  glVertex2fv(v5);
	  glColor3f(0.0,0.0,1.0);
	  glVertex2fv(v6);
	glEnd();

	/* Now draw some quads, choosing a selection of colours */
	glBegin(GL_QUADS);
	  glColor3f(1.0,0.25,1.0);
	  glVertex2f(1.0,0.0);
	  glColor3f(1.0,1.0,0.5);
	  glVertex2f(1.5,0.0);
	  glColor3f(1.0,0.0,0.75);
	  glVertex2f(1.5,0.5);
	  glColor3f(0.0,0.0,1.0);
	  glVertex2f(1.0,0.5);

	  glColor3f(0.0,0.5,0.5);
	  glVertex2f(1.0,0.75);
	  glColor3f(1.0,0.75,0.5);
	  glVertex2f(1.75,0.75);
	  glColor3f(1.0,1.0,0.25);
	  glVertex2f(1.85,1.25);
	  glColor3f(0.0,1.0,0.0);
	  glVertex2f(1.5,1.5);
	glEnd();

	/* Now for an arbitrary quad strip */
	glBegin(GL_QUAD_STRIP);
	  glColor3f(0.0,1.0,1.0);
	  glVertex2f(-1.75,-0.5);
	  glColor3f(1.0,0.0,1.0);
	  glVertex2f(-1.75,-1.25);
	  glColor3f(0.0,0.5,0.0);
	  glVertex2f(-1.25,-0.75);
	  glColor3f(0.0,0.0,1.0);
	  glVertex2f(-1.5,-1.5);
	  glColor3f(0.5,1.0,0.0);
	  glVertex2f(-0.75,-0.5);
	  glColor3f(0.0,1.0,0.0);
	  glVertex2f(-1.0,-1.5);
	  glColor3f(1.0,1.0,0.0);
	  glVertex2f(-0.5,-0.75);
	  glColor3f(1.0,0.0,0.0);
	  glVertex2f(-0.75,-1.5);
	  glColor3f(0.0,0.0,0.5);
	  glVertex2f(0.0,-0.75);
	  glColor3f(0.0,0.0,0.0);
	  glVertex2f(0.0,-1.75);
	glEnd();

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

void init( void )
{
        glClearColor( 1.0, 1.0, 1.0, 1.0);

		glLineWidth(3.0);

		/* Set a viewing volume for the data we wish to display  */

		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0);
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();	 

}

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

	glutInit( &argc, argv );

	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
	glutCreateWindow( argv[0] );

	printHelp( );

    glutKeyboardFunc( keyboard );
    glutSpecialFunc( specialkeys );

	glutDisplayFunc( display );

	init();

	glutMainLoop();

	return 0;
}