/* Dibujo de linea */

#include <stdlib.h>
#include <GL/glut.h>

/* arreglo N x M */

#define N 400
#define M 400

int n=N;
int m=M;

/* Use unsigned bytes for image */
GLubyte image[N][M][3];

lineaBresenham (int x1, int y1, int x2, int y2) 
{
  int dx, dy, x, y, *dep, *ind, incDep, incInd, incP1, incP2,
    p, escalones, i, sdx, sdy,t;

  if (x1<x2 && y1 > y2) { 
    t=x1; 
    x1=x2;
    x2=t; 
    t=y1; 
    y1=y2;
    y2=t; 
  } 

  dx = abs(x2-x1);
  dy = abs(y2-y1);

  if (dx) {
    sdx = dx/(x2-x1);
  }
  else {
    sdx = 0;
  }

  if (dy) {
    sdy = dy/(y2-y1);
  }
  else {
    sdy = 0;
  }

  if (dx > dy) {
    escalones = dx;
    incP1 = dy*2;
    incP2 =  incP1 - 2*dx;
    p = incP1 - dx;

    dep = &y;
    ind = &x;
    incDep = sdy;

    if (x2<x1) {
      x = x2;
      y = y2;
    }
    else {
      x = x1;
      y = y1;
    }	
  }
  else {
    escalones = dy;
    incP1 = dx*2;
    incP2 = incP1 - 2*dy ;
    p = incP1 - dy;
    dep = &x;
    ind = &y;
    incDep = sdx;

    if (y2<y1) {
      x = x2;
      y = y2;
    }
    else {
      x = x1;
      y = y1;
    }

  }
  incInd = 1;

  /*	x = x1; y = y1; */
  image[(int)y][(int)x][0]=0;
  image[(int)y][(int)x][1]=0;
  image[(int)y][(int)x][2]=0;
	
  /* printf ("\n\n dx: %i\n dy: %i\n x: %i\n y: %i\n *dep: %i\n *ind: %i\n incDep: %i\n incInd: %i\n incP1: %i\n incP2: %i\n p: %i\n escalones: %i\n sdx: %i\n sdy: %i\n", dx, dy, x, y, *dep, *ind, incDep, incInd, incP1, incP2,
	p, escalones, sdx, sdy);*/

  if (dx || dy) {
    for (i=0; i<escalones; i++) {
      *ind += incInd;
      if (p<0) {
		p += incP1;
      }
      else {
		*dep += incDep;
		p += incP2;
      }
	  image[(int)y][(int)x][0]=0;
	  image[(int)y][(int)x][1]=0;
	  image[(int)y][(int)x][2]=0;
    }
  }
}
	
void display(void)
{
    glClearColor (1.0, 1.0, 1.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
	lineaBresenham(5,395,200,5);
    glDrawPixels(n,m,GL_RGB, GL_UNSIGNED_BYTE, image);
	glFlush();
}

void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
		gluOrtho2D(0.0, 0.0, (GLfloat) n, (GLfloat) m* (GLfloat) h / (GLfloat) w);
    else
		gluOrtho2D(0.0, 0.0, (GLfloat) n * (GLfloat) w / (GLfloat) h,(GLfloat) m);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

myinit()
{
	int i,j,k;

	for (i=0;i<n;i++)
		for (j=0;j<m;j++)
			for (k=0;k<3;k++)
				image[i][j][k]=255;
}

main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );
    glutInitWindowSize(N, M);
    glutCreateWindow("linea");
	myinit();
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
    glutMainLoop();
}