diff --git a/README.md b/README.md
index 71ff3f9..3cc1ade 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,7 @@ $ make && ./solar-system
 * `0` à `9` pour visualiser en grand chaque astre.
 * `R` pour reprendre le contrôle (recover) du point précédant.
 * `O` pour toggle mode overview (vue de haut).
+* `Q` pour quitter.
 
 * `L` pour désactiver/activer la lumière.
 * `C` pour activer/désactiver l'utilisation de la couleur.
diff --git a/window.c b/window.c
index 3109d82..5fcc011 100644
--- a/window.c
+++ b/window.c
@@ -33,12 +33,15 @@ static int get_sign(float x, float y);
 /*!\brief un identifiant pour l'écran (de dessin) */
 static uint _screenId = 0;
 
-/*!\brief une surface représentant une sphere */
+// surface representing the Sun.
 static surface_t * _sun = NULL;
+
+// surface array representing 8 planets + pluto (dwarf planet).
 static surface_t * _planet[9] = { 	NULL, NULL, NULL,
 									NULL, NULL, NULL,
 									NULL, NULL, NULL };
 
+// surface array representing 18 moons of the planets.
 static surface_t * _moon[18] = {NULL, NULL, NULL, NULL,
 								NULL, NULL, NULL, NULL,
 								NULL, NULL, NULL, NULL,
@@ -50,6 +53,7 @@ static int _use_tex = 1, _use_color = 0, _use_lighting = 1;
 
 typedef struct cam_t cam_t;
 
+// camera structure, borrowed from sample3d_01-1.6 of GL4Dummies samples.
 struct cam_t {
 	float x, y, z;
 	float theta;
@@ -57,17 +61,21 @@ struct cam_t {
 
 static cam_t _cam = {0, 1.0f, 10, 0};
 
+// movement speed.
 static float _v = 0.1f;
 
+// window size.
 static int _wW = 1200, _wH = 900;
-static int _xm = 400, _ym = 300;
 
-static int _pause = 0;
-static float _s = 1.0f;
-static int _movement = 1;
-static int _p = -1;
-static float _a = 0.0f;
-static int _overview = 0;
+// middle of the window.
+static int _xm = 600, _ym = 450;
+
+static int _pause = 0; // boolean value for the pause.
+static float _s = 1.0f; // multiplier for angle (for speeding planets movement and rotation).
+static int _movement = 1; // boolean to allow movement.
+static int _p = -1; // the object (sun, planets, pluto) number to move.
+static float _a = 0.0f; // rotation angle.
+static int _overview = 0; // boolean to toggle overview (view from the top).
 
 /*!\brief paramètre l'application et lance la boucle infinie. */
 int main(int argc, char ** argv) {
@@ -103,8 +111,9 @@ int main(int argc, char ** argv) {
  * utilisées dans ce code */
 void init(void) {
 	uint id[9], sun_id, i, moon_id[18];
-
-	_sun = mkSphere(12, 12);  /*ça fait 12x12x2 trianles !*/
+	
+	// create all spheres.
+	_sun = mkSphere(12, 12);  /*ça fait 12x12x2 triangles !*/
 	for(i = 0; i < 18; ++i) {
 		_moon[i] = mkSphere(12, 12);
 	}
@@ -112,6 +121,7 @@ void init(void) {
 		_planet[i] = mkSphere(12, 12);
 	}
 
+	// get all textures.
 	sun_id 	= getTexFromBMP("images/2k-sun.bmp");
 	id[0] 	= getTexFromBMP("images/2k-mercury.bmp");
 	id[1] 	= getTexFromBMP("images/2k-venus-surface.bmp");
@@ -123,6 +133,7 @@ void init(void) {
 	id[7] 	= getTexFromBMP("images/2k-neptune.bmp");
 	id[8] 	= getTexFromBMP("images/pluto.bmp");
 	// https://upload.wikimedia.org/wikipedia/commons/4/4f/Moons_of_solar_system_v7.jpg
+	// most of the biggest moons are here.
 	moon_id[0] 	= getTexFromBMP("images/2k-moon.bmp");
 	moon_id[1] 	= getTexFromBMP("images/moons/phobos.bmp");
 	moon_id[2] 	= getTexFromBMP("images/moons/deimos.bmp");
@@ -142,6 +153,7 @@ void init(void) {
 	moon_id[16] = getTexFromBMP("images/moons/triton.bmp");
 	moon_id[17] = getTexFromBMP("images/moons/charon.bmp");
 
+	// set texture to an object id and set all options.
 	setTexId(_sun, sun_id);
 	for(i = 0; i < 18; ++i)
 		setTexId(_moon[i], moon_id[i]);
@@ -170,73 +182,76 @@ void init(void) {
 	atexit(sortie);
 }
 
+// get sign for further move calculation.
 static int get_sign(float x, float y) {
 	if (x > y)
 		return 1;
 	return -1;
 }
 
+// move to the coordinate.
 static void move_to(float posx, float posy , float posz){
-	float epsilon = 0.1f;
-	if (fabsf(_cam.x - posx) > epsilon){
-		_cam.x = _cam.x - (get_sign(_cam.x, posx) * 0.2f);
+	float epsilon = 0.1f; // precision for comparing
+	if (fabsf(_cam.x - posx) > epsilon) {
+		_cam.x = _cam.x - (get_sign(_cam.x, posx) * 0.09f);
 	}
-	if (fabsf(_cam.y - posy) > epsilon){
-		_cam.y = _cam.y - (get_sign(_cam.y, posy) * 0.2f);
+	if (fabsf(_cam.y - posy) > epsilon) {
+		_cam.y = _cam.y - (get_sign(_cam.y, posy) * 0.09f);
 	}
-	if (fabsf(_cam.z - posz) > epsilon){
-		_cam.z = _cam.z - (get_sign(_cam.z, posz) * 0.2f);
+	if (fabsf(_cam.z - posz) > epsilon) {
+		_cam.z = _cam.z - (get_sign(_cam.z, posz) * 0.09f);
 	}
 }
 
+// go to a choosen object (planet, star, pluto(dwarf))
 static void goto_obj(float * mvMat) {
 	switch (_p) {
-		case 1:
-			_a = 0;
+		case 1: // MERCURY
+			_a = 0; // reset angle to 0.
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 4.2f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(4.2f, 1.0f, 0.5f);
 			break;
-		case 2:
+		case 2: // VENUS
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 7.9f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(7.9f, 1.0f, 1.0f);
 			break;
-		case 3:
+		case 3: // EARTH
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 10.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(10.0f, 1.0f, 1.0f);
 			break;
-		case 4:
+		case 4: // MARS
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 15.2f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(15.2f, 1.0f, 0.5f);
 			break;
-		case 5:
+		case 5: // JUPITER
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 30.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(30.0f, 1.0f, 5.0f);
 			break;
-		case 6:
+		case 6: // SATURN
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 50.4f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(50.4f, 1.0f, 5.0f);
 			break;
-		case 7:
+		case 7: // NEPTUNE
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 65.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(65.0f, 1.0f, 5.0f);
 			break;
-		case 8:
+		case 8: // URANUS
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 75.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(75.0f, 1.0f, 4.0f);
 			break;
-		case 9:
+		case 9: // PLUTO
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 85.4f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(85.4f, 1.0f, 0.1f);
 			break;
-		case 0:
+		case 0: // SUN
 			_a = 0;
 			lookAt(mvMat, _cam.x, _cam.y, _cam.z, 0, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 			move_to(0.0f, 1.0f, 10.0f);
@@ -340,7 +355,7 @@ void draw(void) {
 	// Io
 	rotate(nmv, r * 3.0f, 0.0f, 0.1f, 0.0f);
 	translate(nmv, 3.0f, 0.0f, 0.0f);
-	scale(nmv, (1/11.2f), (1/11.2f), (1/11.2f)); // 1/11.2f -> Jupiter is bigger then earth 11.2x / 50 io ~= moon size.
+	scale(nmv, (1/11.2f), (1/11.2f), (1/11.2f));
 	transform_n_raster(_moon[3], nmv, projMat);
 
 	memcpy(nmv, cpy, sizeof nmv);
@@ -487,7 +502,7 @@ void draw(void) {
 	gl4dpScreenHasChanged();
 	/* fonction permettant de raffraîchir l'ensemble de la fenêtre*/
 	gl4dpUpdateScreen(NULL);
-	if (_pause != 1){
+	if (!_pause){
 		_a += ((360.0 * dt) / 60) * _s; // 360 in 1 minute so 1 day = 1 min
 		r += ((360.0 * dt) / 60) * _s; // 360 in 1 minute so 1 day = 1 min
 	}
@@ -574,7 +589,8 @@ void key(int keycode) {
 			_pause = 0;
 			_movement = 1;
 			break;
-		case GL4DK_z:
+		case GL4DK_q:
+			exit(0);
 			break;
 		case GL4DK_0:
 			_p = 0;
@@ -708,6 +724,7 @@ void key(int keycode) {
 	}
 }
 
+// handler of mouse motion.
 static void pmotion(int x, int y) {
 	if (_movement){
 		_xm = x;
@@ -716,6 +733,7 @@ static void pmotion(int x, int y) {
 	}
 }
 
+// handler of mouse buttons.
 static void mouse(int button, int state, int x, int y) {
 	if (_movement){
 		double dtheta = M_PI;