diff --git a/main.c b/main.c
index f77d3d8..c6ba9e5 100755
--- a/main.c
+++ b/main.c
@@ -293,13 +293,25 @@ SDL_Surface* initSDL(int width, int height, int fullscreen)
 	return screen;
 }
 
+int screen_to_img(int pos_screen, int zoom ,int offset){
+	return pos_screen/zoom + offset;
+}
+
 void render(SDL_Surface* screen, int x_offset, int y_offset, int zoom_level){
 	int i, j, x, y;
+	int pos_x,pos_y;
+	pos_x = x_offset - img->w/(2*zoom_level);
+	pos_y = y_offset - img->h/(2*zoom_level);
 	SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format, 0, 0, 0));
 	for(i=0; i<screen->w; i++){
 		for(j=0; j<screen->h; j++){
-			x = (i - img->w/2)/zoom_level + x_offset;
-			y = (j - img->h/2)/zoom_level + y_offset;
+			//new version
+			x = screen_to_img(i,zoom_level,pos_x);
+			y = screen_to_img(j,zoom_level,pos_y);
+			
+			//old version
+			//x = (i - img->w/2 )/zoom_level + x_offset;
+			//y = (j - img->h/2 )/zoom_level + y_offset;
 			if(x >= 0 && x < img->w && y >= 0 && y < img->h)
 				putpixel(screen, i, j, getpixel(img, x, y));
 		}
@@ -315,8 +327,6 @@ int MAIN
 	int x_offset = 0;
 	int y_offset = 0;
 	int zoom_level = 1;
-	int seuil_x; // limit for x_offset
-	int seuil_y; // limit for y_offset
 	int over = 0;
 	int time = 0;
 	int wait_time = 100;
@@ -354,6 +364,7 @@ int MAIN
 	
 	x_offset = width/2;
 	y_offset = height/2;
+	
 	printf("Launching simulation...\n");
 	
 	time = SDL_GetTicks();
@@ -411,19 +422,11 @@ int MAIN
 			}
 		}
 		/* check x and y offset*/
-		seuil_x = width/(2*zoom_level);
-		if (x_offset < seuil_x) x_offset=seuil_x;
-		
-		if (x_offset > width-seuil_x) x_offset=width-seuil_x;
-		
-		seuil_y = height/(2*zoom_level);
-		if (y_offset < seuil_y) y_offset=seuil_y;
-		
-		if(y_offset > height-seuil_y) y_offset=height-seuil_y;
-		  
-		  
-		 /*  */
+		if (x_offset < 0) x_offset=0;
+		if (x_offset > width) x_offset=width;
 		
+		if (y_offset < 0) y_offset=0;
+		if(y_offset > height) y_offset=height;
 		
 		new_time = SDL_GetTicks();
 		remaining_time -= new_time - time;