/*
  Presented by James Madison University Computer Science major Joshua Blake
  to FALL 2004 CS 480 students on 8/31/2004

  UPDATED: 3/1/2004

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

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

float myx, myy;		//position of the vertex
float dx, dy;		//velocity of the vertex


void renderScene(void) {				//draws the 2D scene

	glClear(GL_COLOR_BUFFER_BIT);		//clears the color buffer (default: black)
	glBegin(GL_TRIANGLES);				//begin processing vertices as triangle triples

		glColor3f(1.0, 0.0, 0.0);		//set color to red (R = 1, G = 0, B = 0)
		glVertex3f(myx, myy, 0.0);		//first vertex at (myx, myy, 0)
		
		glColor3f(0.0, 1.0, 0.0);		//set color to green (R = 0, G = 1, B = 0)
		glVertex3f(10.0, 0.0, 0.0);		//second vertex at (10, 0, 0)

		glColor3f(0.0, 0.0, 1.0);		//set color to blue (R = 0, G = 0, B = 1)
		glVertex3f(0.0, 10.0, 0.0);		//third vertex at (0, 10, 0)
		
										/*this completes one triangle
										  further triples of vertices would become
										  separate triangles
										*/
	glEnd();							//end vertex processing

	glFlush();							//flush all primitives to color buffer
										//NOTE: glFlush() is needed in single buffering,
										//but is redundant in double buffering because of glutSwapBuffers()

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

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 'h':				//'h' will print hi to the console
			printf("hi\n");
			break;


		case 'w':				//'w' increases the y velocity
			dy += 0.1;
			break;
		case 's':				//'s' decreases the y velocity
			dy -= 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;
	}

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

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

	myx += dx;						//move the current position by the velocity
	myy += dy;						//in x and y

	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

}

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("My first OpenGL 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
	glutDisplayFunc(renderScene);					//register the display callback

	gluOrtho2D(0, 10, 0, 10);			//Set up an Orthographic Projection in 2D
										// with X ranging from 0 to 10
										// and Y ranging from 0 to 10

	myx = 0.0;							//initial vertex position
	myy = 0.0;

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

	return 0;							//this is never executed
}