diff --git a/doc/005.png b/doc/005.png
new file mode 100644
index 0000000..6360748
Binary files /dev/null and b/doc/005.png differ
diff --git a/tinyraycaster.cpp b/tinyraycaster.cpp
index 3507b15..9322ffd 100644
--- a/tinyraycaster.cpp
+++ b/tinyraycaster.cpp
@@ -68,6 +68,7 @@ int main() {
     float player_x = 3.456; // player x position
     float player_y = 2.345; // player y position
     float player_a = 1.523; // player view direction
+    const float fov = M_PI/3.; // field of view
 
     for (size_t j = 0; j<win_h; j++) { // fill the screen with color gradients
         for (size_t i = 0; i<win_w; i++) {
@@ -92,14 +93,18 @@ int main() {
     // draw the player on the map
     draw_rectangle(framebuffer, win_w, win_h, player_x*rect_w, player_y*rect_h, 5, 5, pack_color(255, 255, 255));
 
-    for (float t=0; t<20; t+=.05) {
-        float cx = player_x + t*cos(player_a);
-        float cy = player_y + t*sin(player_a);
-        if (map[int(cx)+int(cy)*map_w]!=' ') break;
+    for (size_t i=0; i<win_w; i++) { // draw the visibility cone
+        float angle = player_a-fov/2 + fov*i/float(win_w);
 
-        size_t pix_x = cx*rect_w;
-        size_t pix_y = cy*rect_h;
-        framebuffer[pix_x + pix_y*win_w] = pack_color(255, 255, 255);
+        for (float t=0; t<20; t+=.05) {
+            float cx = player_x + t*cos(angle);
+            float cy = player_y + t*sin(angle);
+            if (map[int(cx)+int(cy)*map_w]!=' ') break;
+
+            size_t pix_x = cx*rect_w;
+            size_t pix_y = cy*rect_h;
+            framebuffer[pix_x + pix_y*win_w] = pack_color(255, 255, 255);
+        }
     }
 
     drop_ppm_image("./out.ppm", framebuffer, win_w, win_h);