Open GL - algoritmos de rotacion

//#include <GL/gl.h>

//#include <GL/glu.h>

#include <GL/glut.h>

#include <thread>

typedef struct{

    float x,y;

}TPoint;

TPoint p1,p2;

int refreshMillis = 100;      // Refresh period in milliseconds

float ax,ay,x,y,res;

int i;

void DDA(int nothing)

{

	p1.x=-10.0; p1.y=-10.0;

	p2.x=10.0; p2.y=10.0;

	float m;

	//calculate the slope and parameter b

	m=(p2.y-p1.y)/(p2.x-p1.x);

	if(abs(p2.x-p1.x)>=abs(p2.y-p1.y))

	//si la variacion en x es mayor o igual que la variacion en y

		res=abs(p2.x-p1.x);

	else

	//si la variacion en y es mayor que la variacion en x

		res=abs(p2.y-p1.y);

	ax=(p2.x-p1.x)/res;//el valor a aumentar en x

	ay=(p2.y-p1.y)/res;//el valor a aumentar en y

	//se realiza casteo a float porque los resultados de la división es un real

	x=(float)p1.x;

	y=(float)p1.y;

}

void Timer(int value)

{

	i=0;

	if(i<=res)

	{

		x=x+ax;

		y=y+ay;

		i++;

	}

	glutPostRedisplay();    // Post a paint request to activate display()

	glutTimerFunc(refreshMillis, Timer, 0); // subsequent timer call at milliseconds	

}

void display(void)

{

	glClear (GL_COLOR_BUFFER_BIT);

	glPushMatrix();

	//std::this_thread::sleep_for(std::chrono::milliseconds(100));

	glBegin(GL_LINE_LOOP);

	glVertex3f(x,y,0.0);

	glVertex3f(x+1,y,0.0);

	glVertex3f(x+1,y+1,0.0);

	glVertex3f(x,y+1,0.0);

	glEnd();

	glPopMatrix();

	glutSwapBuffers();

}

void init (void)

{

    glClearColor (0.0, 0.0, 0.0, 0.0);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    glOrtho(-15.0,15.0,-15.0,15.0,-15.0,15.0);

	glMatrixMode(GL_MODELVIEW);

}

int main(int argc, char** argv)

{

    glutInit(&argc, argv);

    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);

    glutInitWindowSize (400,400);

    glutInitWindowPosition (100,100);

    glutCreateWindow ("Algoritmo DDA");

    DDA(1);

    init ();

    glutTimerFunc(0, Timer, 0);

    glutDisplayFunc(display);

    glutMainLoop();

    return 0;   /* ISO C requires main to return int. */