/*
  Presented by James Madison University Computer Science major Joshua Blake
  to FALL 2004 CS 480 students on 9/7/2004

  Feel free to use and modify as needed.  
  Please send me an email if you find this useful: blakejr@jmu.edu

  This code generates a 3D terrain using OpenGL
*/

#include <gl/glut.h>				//include gl/glut.h in all GLUT programs
#include <stdio.h>

#include <math.h>

#define M_PI       3.14159265358979323846

#define SIZE 50

float points[SIZE][SIZE];

float xpos, ypos, zpos;
float xdir, ydir;

float speed;

float dxdir, dydir;

float dx, dy, dz;

int left_down;

int mouseStartX, mouseStartY;
int mouseCurrentX, mouseCurrentY;

void drawVertex(int i, int j) {
	
	float x, z;
	float xmax, zmax, xmin, zmin, xr, zr;;

	xmax = 5.0;
	xmin = -5.0;
	zmax = 5.0;
	zmin = -5.0;

	xr = xmax - xmin;
	zr = zmax - zmin;

	x = (i/(float)SIZE)*xr + xmin;
	z = (j/(float)SIZE)*zr + zmin;

	glVertex3f(x, points[i][j], z);
}

void drawQuad(int i, int j) {
	glBegin(GL_QUADS);
		drawVertex(i  , j  );
		drawVertex(i+1, j  );
		drawVertex(i+1, j+1);
		drawVertex(i  , j+1);
	glEnd();
}

void drawLines(int i, int j) {
	glBegin(GL_LINE_STRIP);
		drawVertex(i  , j  );
		drawVertex(i+1, j  );
		drawVertex(i+1, j+1);
		drawVertex(i  , j+1);
		drawVertex(i  , j  );
	glEnd();
}


void display(void) {				//draws the scene

	int i, j;

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	

	glPushMatrix();

		glRotatef(ydir, 1, 0, 0);
		glRotatef(xdir, 0, 1, 0);

		glPushMatrix();
			glTranslatef(xpos, zpos, ypos);


		for (i=0; i<SIZE-1; i++) {
			for (j=0; j<SIZE-1; j++) {
				glColor3f(points[i][j], -points[i][j], points[i][j]);
				drawQuad(i, j);

//				glColor3f(1, 1, 1);
//				drawLines(i, j);
			}
		}

		glPopMatrix();
	glPopMatrix();

	glutSwapBuffers();					//swap the front and back buffers in double buffering
}

void specialkey(int key, int x, int y) {

	switch (key) {
		case GLUT_KEY_LEFT:
			dxdir -= 1;
			break;
		case GLUT_KEY_RIGHT:
			dxdir += 1;
			break;
		case GLUT_KEY_DOWN:
			dydir -= 1;
			break;
		case GLUT_KEY_UP:
			dydir += 1;
			break;
		default:
			break;
	}
}

void keyboard(unsigned char key, int x, int y) {	/*key presses are sent here
													  key is the character pressed, 
													  x and y are the mouse position
													  IN WINDOW COORDINATES
													*/

	switch (key) {
		case 'q':			//'q' or ESC will exit the program
		case 27:
			exit(0);
			break;

		case 'w':				//'w' increases the y velocity
			speed += 0.1;
			break;
		case 's':				//'s' decreases the y velocity
			speed -= 0.1;
			break;
/*
		case 'a':				//'a' decreases the x velocity
			dx += 0.1;
			break;
		case 'd':				//'a' increases the x velocity
			dx -= 0.1;
			break;
*/		
		case 'e':
			dz -= 0.1;
			break;
		case 'c':
			dz += 0.1;
			break;

		case 'x':
			speed = 0;
			dz = 0;
			dxdir = 0;
			dydir = 0;
			break;

		case 'f':
			glutFullScreen();
			break;

		case 'p':
			printf("x: %f y: %f z: %f\n", xpos, ypos, zpos);
			break;
	}

	glutPostRedisplay();		//tell GLUT it needs to repaint the window
}

void mouse(int button, int state, int x, int y) {

	if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
		left_down = 1;

		mouseStartX = x;
		mouseStartY = y;
		mouseCurrentX = x;
		mouseCurrentY = y;

	} else if (left_down == 1 && button == GLUT_LEFT_BUTTON && state == GLUT_UP) {
		left_down = 0;

		mouseCurrentX = x;
		mouseCurrentY = y;
		mouseStartX = x;
		mouseStartY = y;
		dxdir = 0;
		dydir = 0;

	}

}

void mouseMotion(int x, int y) {
	if (left_down == 1) {
		mouseCurrentX = x;
		mouseCurrentY = y;
	} else {
		mouseCurrentX = x;
		mouseCurrentY = y;
		mouseStartX = x;
		mouseStartY = y;
	}
}

void timer(int num) {				//timer is called according to the glutTimerFunc() callback

	xpos += -speed*sin(xdir/180.0*M_PI);
	ypos += speed*cos(xdir/180.0*M_PI);
	zpos += dz;

	if (left_down == 1) {
		dxdir = (mouseCurrentX - mouseStartX)/50.0;
		dydir = (mouseCurrentY - mouseStartY)/50.0;
	}

	xdir += dxdir;
	ydir += dydir;

	glutPostRedisplay();			//tell GLUT it needs to repaint the window

	glutTimerFunc(10, timer, 1);	//tell GLUT to call this function again in 10 ms with 1 as the parameter

}

void reshape(int w, int h) {

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(60, (float)w/(float)h, 0.1, 60);

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	glViewport(0, 0, w, h);

	//gluLookAt(0, 2, -10, 0, 0, 0, 0, 1, 0);


}

void init() {

	int i, j;

	glClearColor(0, 0, 0, 0);
	glEnable(GL_DEPTH_TEST);

	for (i=0; i<SIZE; i++) {
		for (j=0; j<SIZE; j++) {
			points[i][j] = (sin((double)i*10.0/SIZE)+sin((double)j*10.0/SIZE))/2.0;
		}
	}

	xpos = 0;
	ypos = -10;
	zpos = -1;
	xdir = 0;
	ydir = 0;

	dxdir = 0;
	dydir = 0;
	dx = 0;
	dy = 0;

	speed = 0;

	left_down = 0;
	mouseCurrentX = 0;
	mouseCurrentY = 0;
	mouseStartX = 0;
	mouseStartY = 0;
}

int main(int argc, char **argv) {

	glutInit(&argc, argv);											//initialize GLUT
	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);		/* display mode:
																		use DEPTH BUFFERING
																		use DOUBLE BUFFERING
																		use RGBA color scheme
																	*/
	glutInitWindowPosition(100,100);				//initial window position
	glutInitWindowSize(800,600);					//initial window size
	glutCreateWindow("Terrain Program");	//create the window with the specified title

	glutTimerFunc(10, timer, 1);					//set the timer callback to fire in 10 milliseconds

	glutKeyboardFunc(keyboard);						//register the keyboard callback
	glutSpecialFunc(specialkey);
	glutDisplayFunc(display);					//register the display callback
	glutReshapeFunc(reshape);

	glutMouseFunc(mouse);
	glutMotionFunc(mouseMotion);

	init();

	glutMainLoop();						//enter the main loop (never returns)

	return 0;							//this is never executed
}