/*   prac2a.c   */

/* 
     Purpose: open a window, clear the background, construct Sierpinski gasket 
*/


#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  */


/* New Types */
typedef struct PointCoord PointCoord;
struct PointCoord
{
	float x;
	float y;
};

/* Module constants and variables  */
const static PointCoord triangle[3]={{-0.8,-0.8},{0.8,-0.8},{0.0,0.8}};



void printHelp( void )
{
	fprintf(stdout,
			"Sierpinski gasket\n\n"
			"SPACE key     - generates 1000 points\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 ' ':           /* Generate another 1000 points */
		glutPostRedisplay();
    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();
	}
}

int myrandom(int m)
{
	return rand()%m;
}


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

	PointCoord point={0.0, 0.8};  /* seed the point generation  */
    int i;
	int k; 

	glClear( GL_COLOR_BUFFER_BIT );


	/* draw outline of initial triangle first */
	glColor3f(1.0,0.0,0.0);
	glLineWidth(5.0);
	glBegin(GL_LINE_LOOP);
	  glVertex2f(triangle[0].x,triangle[0].y);
	  glVertex2f(triangle[1].x,triangle[1].y);
	  glVertex2f(triangle[2].x,triangle[2].y);
	glEnd();

	/* set random colour for points */
	glColor3f(myrandom(10)/10.0,myrandom(10)/10.0,myrandom(10)/10.0);

	glBegin(GL_POINTS);
    for (k=0; k<1000; k++)
	{ 
		i = myrandom(3);
		point.x = (point.x+triangle[i].x)/2;
		point.y = (point.y+triangle[i].y)/2;
		glVertex2f(point.x,point.y);
	} 
	glEnd();

	checkError( "display" );

	glFlush();
}

void init( void )
{
	glClearColor( 1.0, 1.0, 1.0, 1.0);
	glPointSize(3.0);  /* set large point size  */

}

int main( int argc, char *argv[] )
{
	
	glutInit( &argc, argv );
	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );

	glutCreateWindow( argv[0] );

	printHelp();

	glutDisplayFunc( display );

    glutKeyboardFunc( keyboard );
    glutSpecialFunc( specialkeys );

	init();

	glutMainLoop();

	return 0;
}