/* prac7c.c */

/*
	Purpose:  Timings with and without culling
*/



#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 */

#ifdef WIN32
#include <windows.h>
#else
#include <time.h>     /* for the POSIX clock_gettime  */
#endif

/* Global variables  */

static GLfloat mNearClip = 10.0;  /* near clipping plane */
static GLfloat mFarClip  = 20.0;  /* far clipping plane */
static GLboolean mCullOn = GL_FALSE;

void printHelp( void )
{
	fprintf(stdout,
		"\nHidden Surface Culling\n\n"
		"Escape key - exit the program\n\n"
		"Space key - toggle back face culling\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 ' ':
		mCullOn = !mCullOn;
		if (mCullOn)
		{
			glEnable(GL_CULL_FACE);
			printf("Culling On\n");
		}
		else
		{
			glDisable(GL_CULL_FACE);
			printf("Culling Off\n");
		}
		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();
	}
}

/* Return the number of milliseconds from some arbitrary start point */
unsigned int getMilliSecs()
{
#ifdef WIN32
	return GetTickCount();
#else

	/* Make a guess that we are on IRIX */
/*	static timespec_t tp;
	clock_gettime(CLOCK_REALTIME, &tp);

	return tp.tv_sec*1000 + tp.tv_nsec/1000000;
*/
	/* if we are on LINUX comment out the IRIX code and use the following */
	return clock()/CLOCKS_PER_SEC;
#endif
}


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();
	gluPerspective(80, aspect, mNearClip, mFarClip);
	glMatrixMode( GL_MODELVIEW );
}

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

	glCullFace(GL_BACK);

	mCullOn ? glEnable(GL_CULL_FACE) : glDisable(GL_CULL_FACE);
}

GLvoid display( GLvoid )
{
	unsigned int starttime;
	unsigned int endtime;
	int i;
    
	/* Do all your OpenGL rendering here */
	glClear( GL_COLOR_BUFFER_BIT );
	glLoadIdentity();   /* Reset the ModelView transformation every time we draw */

	/* put our model in the middle of the near and far clipping plans */
	glTranslatef(0, 0, -(mNearClip + mFarClip)/2);

	starttime = getMilliSecs();

    glTranslatef(-10, -10, 0);

    for (i=0; i < 400000; i++) {
	   glTranslatef( (GLfloat)i/5000000000, 0, 0);
	   /* Draw front facing polygon  */
       glBegin(GL_TRIANGLES);
          glVertex3f(0.0f, 0.0f, 0.0f);
          glVertex3f(1.0f, 0.0f, 0.0f);
          glVertex3f(1.0f, 1.0f, 0.0f);
       glEnd();
	}
	glTranslatef( -8, 3, 0);
    for (i=0; i < 400000; i++) {
	   glTranslatef( (GLfloat)i/5000000000, 0, 0);
	   /* Draw back facing polygon - should be culled if culling is enabled
			 and CCW vertex ordering is used.  */
       glBegin(GL_TRIANGLES);
          glVertex3f(0.0f, 0.0f, 0.0f);
          glVertex3f(1.0f, 1.0f, 0.0f);
          glVertex3f(1.0f, 0.0f, 0.0f);
       glEnd();
	}

	/* The glFlush function forces execution of OpenGL functions in finite time.
	   However it is asynchronous and returns before all OpenGL execution is complete.
	   glFlush();  */

	/* The glFinish function blocks until all OpenGL execution is complete.  */
	glFinish();
	endtime = getMilliSecs();

	printf("Time for display: %u\n\n", endtime - starttime);

	/* Don't check errors every frame - expensive. Only do it 
	   while debugging.  */
	checkError( "display" );
}

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;
}