diff --git a/buttons.c b/buttons.c
index 90105156..9606662a 100644
--- a/buttons.c
+++ b/buttons.c
@@ -135,7 +135,7 @@ void Button_Message_initial(void)
 
   Display_cursor();
 
-  while(!Get_input() && !Mouse_K && !Key) SDL_Delay(20);
+  while(!Mouse_K && !Key) if(!Get_input()) SDL_Delay(20);
   if (Mouse_K)
     Wait_end_of_click();
 
diff --git a/engine.c b/engine.c
index c8f54883..40b5676b 100644
--- a/engine.c
+++ b/engine.c
@@ -895,8 +895,24 @@ void Main_handler(void)
       }
     }
     }
-    else SDL_Delay(20); // S'il n'y a pas d'évènement, on ne gère pas tout ça et on attend un peu. La partie en dessous doit être exécutée quand
-                     // même pour les trucs asynchrones, par exemple le spray.
+    else
+	{
+		// No event : we go asleep for a while, but we try to get waked up at constant intervals of time
+		// no matter the machine speed or system load. The time is fixed to 10ms (that should be about a cpu slice on most systems)
+		// This allows nice smooth mouse movement.
+    	const int delay = 10;
+
+		Uint32 debut;
+		debut = SDL_GetTicks();
+		// Première attente : le complément de "delay" millisecondes
+		SDL_Delay(delay - (debut % delay));
+		// Si ça ne suffit pas, on complète par des attentes successives de "1ms".
+		// (Remarque, Windows arrondit généralement aux 10ms supérieures)
+		while ( SDL_GetTicks()/delay <= debut/delay)
+		{
+			SDL_Delay(1);
+		}
+	}
 
     // Gestion de la souris
 
diff --git a/operatio.c b/operatio.c
index 0e7667aa..a1454ef4 100644
--- a/operatio.c
+++ b/operatio.c
@@ -39,6 +39,9 @@
     #define M_PI 3.14159265358979323846 
 #endif
 
+/// Time (in SDL ticks) when the next airbrush drawing should be done. Also used for discontinuous freehand drawing.
+Uint32 Airbrush_next_time;
+
 void Start_operation_stack(word new_operation)
 {
   Brush_rotation_center_is_defined=0;
@@ -300,7 +303,7 @@ void Freehand_mode2_1_0(void)
   Operation_push(Paintbrush_X);
   Operation_push(Paintbrush_Y);
   Print_coordinates();
-  SDL_Delay(20);
+  Airbrush_next_time = SDL_GetTicks() + Airbrush_delay*10;
 }
 
 
@@ -319,18 +322,22 @@ void Freehand_mode2_1_2(void)
 
   if ( (start_x!=Paintbrush_X) || (start_y!=Paintbrush_Y) )
   {
-    Hide_cursor();
-    // On affiche définitivement le pinceau
-    Display_paintbrush(Paintbrush_X,Paintbrush_Y,Fore_color,0);
-    Display_cursor();
     Print_coordinates();
-    SDL_Delay(20);
+	if (SDL_GetTicks()>Airbrush_next_time)
+	{
+		Airbrush_next_time+=Airbrush_delay*10;
+    	Hide_cursor();
+    	// On affiche définitivement le pinceau
+    	Display_paintbrush(Paintbrush_X,Paintbrush_Y,Fore_color,0);
+    	Display_cursor();
+	}
   }
 
   Operation_push(Paintbrush_X);
   Operation_push(Paintbrush_Y);
 }
 
+// ----------
 
 void Freehand_mode2_2_0(void)
 //  Opération   : OPERATION_DISCONTINUOUS_DRAW
@@ -342,12 +349,12 @@ void Freehand_mode2_2_0(void)
   Init_start_operation();
   Backup();
   Shade_table=Shade_table_right;
-  // On affiche définitivement le pinceau
-  Display_paintbrush(Paintbrush_X,Paintbrush_Y,Back_color,0);
   Operation_push(Paintbrush_X);
   Operation_push(Paintbrush_Y);
   Print_coordinates();
-  SDL_Delay(20);
+	Airbrush_next_time = SDL_GetTicks() + Airbrush_delay*10;
+  	// On affiche définitivement le pinceau
+ 	Display_paintbrush(Paintbrush_X,Paintbrush_Y,Back_color,0);
 }
 
 
@@ -366,12 +373,15 @@ void Freehand_mode2_2_2(void)
 
   if ( (start_x!=Paintbrush_X) || (start_y!=Paintbrush_Y) )
   {
-    Hide_cursor();
-    // On affiche définitivement le pinceau
-    Display_paintbrush(Paintbrush_X,Paintbrush_Y,Back_color,0);
-    Display_cursor();
     Print_coordinates();
-    SDL_Delay(20);
+	if (SDL_GetTicks()>Airbrush_next_time)
+	{
+		Airbrush_next_time+=Airbrush_delay*10;
+    	Hide_cursor();
+    	// On affiche définitivement le pinceau
+    	Display_paintbrush(Paintbrush_X,Paintbrush_Y,Back_color,0);
+    	Display_cursor();
+	}
   }
 
   Operation_push(Paintbrush_X);
@@ -2042,7 +2052,6 @@ void Curve_3_points_12_11(void)
 
 ///////////////////////////////////////////////////////////// OPERATION_AIRBRUSH
 
-Uint32 Airbrush_next_time;
 void Airbrush_1_0(void)
 //
 //  Opération   : OPERATION_AIRBRUSH