/* prac5b.c     */


/* 
	Purpose: Investigate the difference in the ordering of translate, rotate, and scale. 
*/


#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 for some reason */


/* Global Variables */

static char transformations[3] = {'r', 't', 's'};



/* Functions */

void printHelp( void )
{
	fprintf(stdout, 
		"\nOrder of Transformations\n\n"
                "Escape key - exit the program\n\n"
				"a - swap order of first two transformations\n"
				"s - swap order of last two transformations\n");
}


/* Swap the order of the transformations */
void swap(unsigned short index1, unsigned short index2)
{
	char temp;
	temp = transformations[index1];
	transformations[index1] = transformations[index2];
	transformations[index2] = temp;
}


GLvoid keyboard( GLubyte key, GLint x, GLint y)
{
	switch (key) 
	{
   	case KEY_ESC:   /* exit when escape key is pressed */
		exit(0);
		break;

    case 'a':       /* swap the first two transformations */
		swap(0, 1);
		break;

	case 's':       /* swap the last two transformations */
		swap(1, 2);
		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();
	}
}

void drawAxes(void)
{
	static const GLfloat max = 20.0;
	glBegin(GL_LINES);
		glColor3f(0.0, 0.0, 1.0);
		glVertex2f(-max, 0.0);
		glVertex2f(max, 0.0);
		glColor3f(0.8, 0.0, 1.0);
		glVertex2f(0.0, -max);
		glVertex2f(0.0, max);
	glEnd();
}

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

GLvoid display( GLvoid )
{
	int index;

	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();  
	drawAxes();

	/* Draw the untransformed triangle */
	glColor3f(1.0,1.0,0.0);
	drawTriangle();

	for (index = 0; index < 3; ++index)
	{
		switch (transformations[index])
		{
		case 'r':
			glRotatef(60, 0, 0, 1);
			printf("Rotate\t");
			break;
		case 't':
			glTranslatef(3.0, 0, 0);
			printf("Translate\t");
			break;
		case 's':
			glScalef(3.0, 0.5, 1.0);  
			printf("Scale \t");
			break;
		}
		printf("*\t");
	}
	printf("triangle\n");

	/* Draw the transformed triangle */
	glColor3f(1.0,0.0,0.0);
	drawTriangle();

	checkError( "display" );

	glFlush();

}

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

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-3.0, 13.0, -3.0, 12.0, -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] );

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

	printHelp( );

	glutMainLoop();

	return 0;
}