/* prac5c.c  */


/* 
	Purpose:	use push/pop to change the effective coordinate system. 
*/

#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 */


void printHelp( void )
{
	fprintf(stdout,
		"\nTransformation ordering\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();
	}
}

GLvoid drawTriangle( GLvoid )
{
	glBegin(GL_TRIANGLES);
		glVertex2f(0.0, 1.0);
		glVertex2f(-1.0, -1.0);
		glVertex2f(1.0, -1.0);
	glEnd();
}

/* recursively draw the right branch of the tree */
GLvoid drawRightBranch(int levels)
{	
	if (levels-- > 0) 
	{
		glPushMatrix();
			glTranslatef(1.0, -2.0, 0.0);
			drawTriangle();	
			drawRightBranch(levels);
		glPopMatrix();
	}
}

/* recursively draw the tree */
GLvoid drawTree(int levels)
{
	/* set colour depending on level */
	glColor3f(1.0/levels,0.0,1-1.0/levels);

	/* draw this level */
	drawTriangle();

	if (--levels > 0) 
	{
		/* complete the whole right-most branch descending from here */
		drawRightBranch(levels);

		/* draw the next left branch node */
		glPushMatrix();
			glTranslatef(-1.0, -2.0, 0.0);
			drawTree(levels);
		glPopMatrix();
	}
}

GLvoid display( GLvoid )
{
	glClear( GL_COLOR_BUFFER_BIT );

	/* Do all your OpenGL rendering here */

	/* 
		Set up the transformations.
		We want to start from scratch every time, not build up the transformations 
	*/
	glLoadIdentity();  

	/* Draw the top triangle */
    drawTree(5);
		
	checkError( "display" );

	glFlush();
}


GLvoid init( GLvoid )
{
	glClearColor( 1.0, 1.0, 1.0, 1.0);
	glColor3f(1.0,0.0,0.0);
	glLineWidth(3.0);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-6, 6, -10, 2, -2, 2);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}


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


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

	init();
      
	glutKeyboardFunc( keyboard );
	glutSpecialFunc( specialkeys );
	glutDisplayFunc( display ); 

	printHelp( );

	glutMainLoop();

	return 0;
}