/* prac7a.c  */

/* 
	Purpose:  Investigate viewports and aspect ratios 
*/

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

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

#define KEY_ESC 27      /* glut doesn't define this one for some reason */

void printHelp( void )
{
	fprintf(stdout,
		"\nprac7a - Viewports and aspect ratios\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;

	/* We still want the output to cover the whole window */
	glViewport(0, 0, width, height);

	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();

	/* Get the viewing volume set up to match the aspect ratio of the viewport */
	if (width > height)
	{
		glOrtho(-2 * aspect, 2 * aspect, -2, 2, -2, 2);
	}
	else
	{
		glOrtho(-2, 2, -2 / aspect, 2 / aspect, -2, 2);
	}

	glMatrixMode( GL_MODELVIEW );
}

GLvoid display( GLvoid )
{
	glClear( GL_COLOR_BUFFER_BIT );

	/* Do all your OpenGL rendering here */

	glutWireCube(1.0);

	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);
}

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

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

	init();
   
	glutKeyboardFunc( keyboard );
	glutSpecialFunc( specialkeys );
	glutDisplayFunc( display ); 
/*	glutReshapeFunc( reshape );  */

	printHelp();

	glutMainLoop();

	return 0;
}