diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -54,6 +54,39 @@ And change the map itself :
 # raycasting
 ---
 
+Raycasting is a technic that creates the illusion of 3D with very low computational power.
+
+This technic has the hability to not show hidden area by design, which is a great simplification for rendering.
+
+How it works :
+
+1. first you determine the position and orientation of the viewer in a plan,
+
+![](assets/raycast_step1.png)
+
+2. then you cast a ray until it reaches a wall
+
+![](assets/raycast_step2.png)
+
+3. you can now trace the vertical line on the 3D view
+
+![](assets/raycast_step3.png)
+
+4. the height of the wall is inversely proportional to the length of the ray : the closer the wall, the heigher it is
+
+![](assets/raycast_step4.png)
+
+5. finally, if the rays scan the whole picture, you see the perspective appears
+
+![](assets/raycast_steps.gif)
+
+6. but you can also see that walls are rounded, like a fish eye effect. It's because rays change length while scanning the wall, so we must apply a correction to the angle
+
+![](assets/raycast_steps_round.gif)
+
+example of raycasting in action while construction of the project :
+
+![example of raycasting during the construction of the project](assets/cube3d_raycasting.gif)
 
 
 
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diff --git a/headers/cube3d_macro.h b/headers/cube3d_macro.h
index a25bcca..1bf3e87 100644
--- a/headers/cube3d_macro.h
+++ b/headers/cube3d_macro.h
@@ -34,7 +34,7 @@
 /* size of a cell on the map */
 # define CELL 100
 // minimum time in milliseconds between two keypress
-# define DEBOUNCE_TIME  500
+# define DEBOUNCE_TIME  10
 
 
 /*