/* timer.c  */

/* Program to demonstrate the use of the glutTimerFunc callback.
 * This program uses the glutTimerFunc to update a variable at
 * regular intervals. Note that the callback must be re-set after the
 * timer function has been called if you want it to call again.
 *
 * Note also the resize behaviour of this program. Can you modify the
 * program so the text always begins at the top left of the screen,
 * regardless of window size?
 *
 * As another exercise, modify the program so that the 's' key starts
 * and stops the timer (press 's' to start, 's' again to stop) and displays
 * a "timer paused" message when stopped. Use the 'r' key to reset the 
 * counter to 0.
 *
 */


/* Copyright Jon McCormack, March 2004 */
/* Updated 29 March 2004: Removed platform dependencies */

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

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

#define MAX_TEXT_SIZE		255			/* maximum text string length */
#define GAP					1000		/* ms gap between updates */

/*
 * static shared variables
 */
static int g_counter = 0;

/*
 * drawText
 *
 * Draws the specified message in both
 * raster and stroke text
 *
 */
void drawText(const char * message, GLfloat x, GLfloat y)
{
	/* raster pos sets the current raster position
	 * mapped via the modelview and projection matrices
	 */
	glRasterPos2f(x, y);

	/*
	 * write using bitmap and stroke chars
	 */
	while (*message) {
		glutBitmapCharacter(GLUT_BITMAP_HELVETICA_12, *message++);
	}
}

/*
 * display
 *
 * This function is called by the GLUT to display the graphics
 * In this case it clears the screen then calls the function "drawText"
 * which will draw some text using GLUT
 *
 */
void display(void) {

	char text[MAX_TEXT_SIZE];
	sprintf(text,"%d seconds have elapsed.", g_counter);
    glClear( GL_COLOR_BUFFER_BIT );
 	drawText(text, -2.0, 1);
	drawText("Press q to quit", -2.0, 0);

 	glFlush(); /* force OpenGL output */
}


/*
 * myReshape
 *
 * This function is called whenever the user (or OS) reshapes the
 * OpenGL window. The GLUT sends the new window dimensions (x,y)
 *
 */
void myReshape(int w, int h)
{
	/* set viewport to new width and height */
	/* note that this command does not change the CTM */
    glViewport(0, 0, w, h);

	/* 
	 * set viewing window in world coordinates 
	 */
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); /* init projection matrix */

    if (w <= h)
        glOrtho(-2.0, 2.0, -2.0 * (GLfloat) h / (GLfloat) w,
            2.0 * (GLfloat) h / (GLfloat) w, -1.0, 1.0);
    else
        glOrtho(-2.0 * (GLfloat) w / (GLfloat) h,
            2.0 * (GLfloat) w / (GLfloat) h, -2.0, 2.0, -1.0, 1.0);

	/* set matrix mode to modelview */
    glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

/*
 * myTimer
 *
 * Called by the glutTimerFunc callback. This function increments the
 * supplied parameter value, storing it in g_counter. We then call
 * glutPostRedisplay() to force the glut to re-display the screen (which will
 * update the time displayed. The timer callback only calls the supplied
 * function once, so if we want repeated calls we must set the callback
 * again after each call.
 */
void myTimer(int value) {
	g_counter = value + 1; 
	glutPostRedisplay();
	glutTimerFunc(GAP, myTimer, g_counter);
}

/*
 * myKey
 *
 * responds to key presses from the user
 */
void myKey(unsigned char k, int x, int y)
{
	switch (k) {
		case 'q':
		case 'Q':	
			exit(0);
			break;
		default:
			printf("Unknown keyboard command \'%c\'.\n", k);
			break;
	}
}


/*
 * main
 *
 * Initialization and sets graphics callbacks
 *
 */
int main(int argc, char **argv)
{
	/* glutInit MUST be called before any other GLUT/OpenGL calls */
    glutInit(&argc, argv);

	/* need both double buffering and z buffer */

    glutInitDisplayMode(GLUT_RGB);
    glutInitWindowSize(400, 100);
    glutCreateWindow("The Timer");

	/* set callback functions */
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
	glutKeyboardFunc(myKey);
	glutTimerFunc(GAP, myTimer, 0);

	/* set clear colour */
	glClearColor(1.0, 1.0, 1.0, 1.0);

	/* set current colour to black */
	glColor3f(0.0, 0.0, 0.0);

    glutMainLoop();

	return 0;
}