diff --git a/src/game.c b/src/game.c
index 0111ccc5f8..a194780414 100644
--- a/src/game.c
+++ b/src/game.c
@@ -286,13 +286,6 @@ void game_logic_update()
 	if (RCT2_GLOBAL(0x009DEA66, sint16) == 0)
 		RCT2_GLOBAL(0x009DEA66, sint16)--;
 
-	// This is a hack for now to force a complete rerender of the screen to 
-	// stop viewports from failing. Remove this when real bug cause has been 
-	// found.
-	// ***********
-	//gfx_invalidate_screen();
-	// ***********
-
 	sub_68B089();
 	scenario_update();
 	climate_update();
diff --git a/src/interface/viewport.c b/src/interface/viewport.c
index 9a26119f5b..5bddfcbf2a 100644
--- a/src/interface/viewport.c
+++ b/src/interface/viewport.c
@@ -33,7 +33,7 @@
 #define RCT2_LAST_VIEWPORT		(RCT2_GLOBAL(RCT2_ADDRESS_NEW_VIEWPORT_PTR, rct_viewport*) - 1)
 #define RCT2_NEW_VIEWPORT		(RCT2_GLOBAL(RCT2_ADDRESS_NEW_VIEWPORT_PTR, rct_viewport*))
 
-#define DEBUG_SHOW_DIRTY_BOX
+//#define DEBUG_SHOW_DIRTY_BOX
 
 rct_viewport* g_viewport_list = RCT2_ADDRESS(RCT2_ADDRESS_VIEWPORT_LIST, rct_viewport);
 
@@ -214,8 +214,9 @@ void viewport_update_pointers()
 	rct_viewport *viewport;
 	rct_viewport **vp = RCT2_ADDRESS(RCT2_ADDRESS_NEW_VIEWPORT_PTR, rct_viewport*);
 
-	if (*vp == NULL) *vp = g_viewport_list;
-	for (viewport = g_viewport_list; viewport <= RCT2_NEW_VIEWPORT; viewport++)
+	// The last possible viewport entry is 1 before what is the new_viewport_ptr
+	// This is why it is rct_viewport and not rct_viewport*.
+	for (viewport = g_viewport_list; viewport < RCT2_ADDRESS(RCT2_ADDRESS_NEW_VIEWPORT_PTR, rct_viewport); viewport++)
 		if (viewport->width != 0)
 			*vp++ = viewport;
 
@@ -266,39 +267,38 @@ void sub_689174(sint16* x, sint16* y, sint16 *z, uint8 curr_rotation){
 	*z = height;
 }
 
-// This function also needs edx, ebp
-void sub_6E7FF3(rct_window* w, rct_viewport* viewport, int x, int y){
-	int zoom = 1 << viewport->zoom;
-	if (w >= RCT2_GLOBAL(RCT2_ADDRESS_NEW_WINDOW_PTR, rct_window*)){
-		if (viewport != w->viewport){
-			if ((viewport->x + viewport->width > w->x) &&
-				(w->x + w->width > viewport->x) &&
-				(viewport->y + viewport->height > w->y) &&
-				(w->y + w->height > viewport->y)){
-				if (viewport->x < w->x){
-					rct_viewport viewport_bkup;
-					memcpy(&viewport_bkup, viewport, sizeof(rct_viewport));
-
-					viewport->width = w->x - viewport->x;
-					viewport->view_width = (w->x - viewport->x) * zoom;
-
-					sub_6E7FF3(w, viewport, x, y);
-					
-					viewport->x += viewport->width;
-					viewport->view_x += viewport->width*zoom;
-					viewport->view_width = (viewport_bkup.width - viewport->width) * zoom;
-					viewport->width = viewport_bkup.width - viewport->width;
-					
-					sub_6E7FF3(w, viewport, x, y);
-
-					memcpy(viewport, &viewport_bkup, sizeof(rct_viewport));
-					return;
-				}//x6E80C4
-			}//0x6E824a
-		} // 0x6e824a
-	}//x6e8255
-
-}
+//void sub_6E7FF3(rct_window* w, rct_viewport* viewport, int x, int y){
+//	int zoom = 1 << viewport->zoom;
+//	if (w >= RCT2_GLOBAL(RCT2_ADDRESS_NEW_WINDOW_PTR, rct_window*)){
+//		if (viewport != w->viewport){
+//			if ((viewport->x + viewport->width > w->x) &&
+//				(w->x + w->width > viewport->x) &&
+//				(viewport->y + viewport->height > w->y) &&
+//				(w->y + w->height > viewport->y)){
+//				if (viewport->x < w->x){
+//					rct_viewport viewport_bkup;
+//					memcpy(&viewport_bkup, viewport, sizeof(rct_viewport));
+//
+//					viewport->width = w->x - viewport->x;
+//					viewport->view_width = (w->x - viewport->x) * zoom;
+//
+//					sub_6E7FF3(w, viewport, x, y);
+//					
+//					viewport->x += viewport->width;
+//					viewport->view_x += viewport->width*zoom;
+//					viewport->view_width = (viewport_bkup.width - viewport->width) * zoom;
+//					viewport->width = viewport_bkup.width - viewport->width;
+//					
+//					sub_6E7FF3(w, viewport, x, y);
+//
+//					memcpy(viewport, &viewport_bkup, sizeof(rct_viewport));
+//					return;
+//				}//x6E80C4
+//			}//0x6E824a
+//		} // 0x6e824a
+//	}//x6e8255
+//
+//}
 
 void sub_6E7F34(rct_window* w, rct_viewport* viewport){
 	//RCT2_CALLPROC_X(0x6E7F34, 0, 0, 0, 0, (int)viewport, (int)w, 0);
@@ -333,7 +333,7 @@ void sub_6E7F34(rct_window* w, rct_viewport* viewport){
 	}
 
 	w = orignal_w;
-	RCT2_CALLPROC_X(0x6E7FF3, 0, 0, 0, right, viewport, w, bottom);
+	RCT2_CALLPROC_X(0x6E7FF3, 0, 0, 0, right, (int)viewport, (int)w, bottom);
 }
 
 void sub_6E7DE1(sint16 x, sint16 y, rct_window* w, rct_viewport* viewport){
diff --git a/src/peep/peep.c b/src/peep/peep.c
index 0571b422a5..13691c1585 100644
--- a/src/peep/peep.c
+++ b/src/peep/peep.c
@@ -107,6 +107,48 @@ void peep_update_all()
 	}
 }
 
+/* rct2: 0x006EC473 */
+void invalidate_sprite(rct_peep* peep){
+	if (peep->var_16 == (sint16)0x8000) return;
+
+	// Note this function is different to original perhaps change back (part of viewport testing)
+	for (rct_viewport* viewport = RCT2_ADDRESS(RCT2_ADDRESS_VIEWPORT_LIST, rct_viewport); viewport < RCT2_ADDRESS(RCT2_ADDRESS_NEW_VIEWPORT_PTR, rct_viewport) && viewport->width; viewport++){
+		int left, right, top, bottom;
+		left = peep->var_16;
+		right = peep->var_1A;
+		top = peep->var_18;
+		bottom = peep->var_1C;
+
+		if (viewport->zoom >= 3)continue;
+		if (right <= viewport->view_x)continue;
+		if (bottom <= viewport->view_y) continue;
+
+		int viewport_right = viewport->view_x + viewport->view_width;
+		int viewport_bottom = viewport->view_y + viewport->view_height;
+
+		if (left >= viewport_right)continue;
+		if (top >= viewport_bottom)continue;
+
+		left = max(left, viewport->view_x);
+		right = min(right, viewport_right);
+		top = max(top, viewport->view_y);
+		bottom = min(bottom, viewport_bottom);
+
+		left -= viewport->view_x;
+		top -= viewport->view_y;
+		right -= viewport->view_x;
+		bottom -= viewport->view_y;
+
+		int zoom = 1 << viewport->zoom;
+		left /= zoom;
+		top /= zoom;
+		right /= zoom;
+		bottom /= zoom;
+
+		gfx_set_dirty_blocks(left + viewport->x, top + viewport->y, right + viewport->x, bottom + viewport->y);
+	}
+}
+
 /* rct2: 0x6939EB */
 int sub_6939EB(sint16* x, sint16* y, rct_peep* peep){
 	RCT2_GLOBAL(0xF1AEF0, uint8) = peep->var_70;
@@ -163,14 +205,14 @@ int sub_6939EB(sint16* x, sint16* y, rct_peep* peep){
 		peep->var_70 = 0;
 		peep->var_71 = 0xFF;
 		RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);
 		*x = peep->x;
 		*y = peep->y;
 		return 1;
 	}
 	peep->var_70 = ebx;
 	if (peep->var_71 != 8 || peep->var_71 != 15){
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);
 		*x = peep->x;
 		*y = peep->y;
 		return 1;
@@ -192,7 +234,7 @@ int sub_6939EB(sint16* x, sint16* y, rct_peep* peep){
 
 	sound_play_panned(sound_id, 0x8001, peep->x, peep->y, peep->z);
 
-	RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+	invalidate_sprite(peep);;
 	*x = peep->x;
 	*y = peep->y;
 	return 1;
@@ -310,7 +352,7 @@ void peep_update_falling(rct_peep* peep){
 
 				if (height - 4 >= peep->z && height < peep->z + 20){
 					// Looks like we are drowning!
-					RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+					invalidate_sprite(peep);;
 					sub_69E9D3(peep->x, peep->y, height, (rct_sprite*)peep);
 					// Drop balloon if held
 					if (peep->item_standard_flags & PEEP_ITEM_BALLOON){
@@ -330,7 +372,7 @@ void peep_update_falling(rct_peep* peep){
 					peep->var_70 = 0;
 
 					RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-					RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+					invalidate_sprite(peep);;
 					peep_window_state_update(peep);
 					return;
 				}
@@ -345,20 +387,20 @@ void peep_update_falling(rct_peep* peep){
 
 	// This will be null if peep is falling
 	if (saved_map == NULL){
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		if (peep->z <= 1){
 			// Remove peep if it has gone to the void
 			peep_remove(peep);
 			return;
 		}
 		sub_69E9D3(peep->x, peep->y, peep->z - 2, (rct_sprite*)peep);
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		return;
 	}
 	
-	RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+	invalidate_sprite(peep);;
 	sub_69E9D3(peep->x, peep->y, saved_height, (rct_sprite*)peep);
-	RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+	invalidate_sprite(peep);;
 
 	peep->next_x = peep->x & 0xFFE0;
 	peep->next_y = peep->y & 0xFFE0;
@@ -412,11 +454,11 @@ void peep_update_sitting(rct_peep* peep){
 		int y = peep->y & 0xFFE0 + RCT2_ADDRESS(0x981F2E, uint16)[ebx * 2];
 		int z = peep->z;		
 		
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		sub_69E9D3(x, y, z, (rct_sprite*)peep);
 
 		peep->sprite_direction = ((peep->var_37 + 2) & 3) * 8;
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		peep->var_71 = 254;
 		peep->var_6F = 7;
 		RCT2_CALLPROC_X(0x693BAB, 0, 0, 0, 0, (int)peep, 0, 0);
@@ -466,7 +508,7 @@ void peep_update_sitting(rct_peep* peep){
 			peep->var_72 = 0;
 			peep->var_70 = 0;
 			RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-			RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+			invalidate_sprite(peep);;
 			return;
 		}
 
@@ -491,7 +533,7 @@ void peep_update_sitting(rct_peep* peep){
 		peep->var_72 = 0;
 		peep->var_70 = 0;
 		RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		return;
 	}
 }
@@ -525,7 +567,7 @@ void peep_update_queuing(rct_peep* peep){
 		}
 		//Give up queueing for the ride
 		peep->sprite_direction ^= (1 << 4);
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		RCT2_CALLPROC_X(0x6966A9, 0, 0, 0, 0, (int)peep, 0, 0);
 		peep_decrement_num_riders(peep);
 		peep->state = PEEP_STATE_1;
@@ -541,7 +583,7 @@ void peep_update_queuing(rct_peep* peep){
 			peep->var_72 = 0;
 			peep->var_70 = 0;
 			RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-			RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+			invalidate_sprite(peep);;
 		}
 		if (peep->var_7A >= 3500 && (0xFFFF & scenario_rand()) <= 93)
 		{
@@ -579,7 +621,7 @@ void peep_update_queuing(rct_peep* peep){
 				peep->var_72 = 0;
 				peep->var_70 = 0;
 				RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-				RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+				invalidate_sprite(peep);;
 				break;
 			}
 		}
@@ -589,7 +631,7 @@ void peep_update_queuing(rct_peep* peep){
 	if (peep->happiness <= 65 && (0xFFFF & scenario_rand()) < 2184){
 		//Give up queueing for the ride
 		peep->sprite_direction ^= (1 << 4);
-		RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);;
 		RCT2_CALLPROC_X(0x6966A9, 0, 0, 0, 0, (int)peep, 0, 0);
 		peep_decrement_num_riders(peep);
 		peep->state = PEEP_STATE_1;
@@ -622,9 +664,9 @@ static void peep_update_entering_park(rct_peep* peep){
 	}
 	sint16 x = 0, y = 0;
 	if (sub_6939EB(&x, &y, peep)){
-		RCT2_CALLPROC_X(0x006EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep); 
 		sub_69E9D3(x, y, peep->z, (rct_sprite*)peep);
-		RCT2_CALLPROC_X(0x006EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+		invalidate_sprite(peep);
 		return;
 	}
 	peep_decrement_num_riders(peep);
@@ -1048,7 +1090,7 @@ void peep_applause()
 			peep->var_72 = 0;
 			peep->var_70 = 0;
 			RCT2_CALLPROC_X(0x00693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-			RCT2_CALLPROC_X(0x006EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+			invalidate_sprite(peep);
 		}
 	}
 
@@ -1432,7 +1474,7 @@ void peep_insert_new_thought(rct_peep *peep, uint8 thought_type, uint8 thought_a
 			peep->var_72 = 0;
 			peep->var_70 = 0;
 			RCT2_CALLPROC_X(0x693B58, 0, 0, 0, 0, (int)peep, 0, 0);
-			RCT2_CALLPROC_X(0x6EC473, 0, 0, 0, 0, (int)peep, 0, 0);
+			invalidate_sprite(peep);;
 	}
 	
 	for (int i = 0; i < PEEP_MAX_THOUGHTS; ++i){