diff --git a/src/interface/viewport.c b/src/interface/viewport.c
index 7a6d591cac..59b7e387ea 100644
--- a/src/interface/viewport.c
+++ b/src/interface/viewport.c
@@ -1453,18 +1453,55 @@ void viewport_paint(rct_viewport* viewport, rct_drawpixelinfo* dpi, int left, in
 	//RCT2_CALLPROC_X(0x00685CBF, left, top, 0, right, (int)viewport, (int)dpi, bottom);
 }
 
+/**
+ *
+ *  rct2: 0x00688972
+ *  In:
+ *		screen_x: eax
+ *		screen_y: ebx
+ *  Out:
+ *		x: ax
+ *		y: bx
+ *		map_element: edx ?
+ *		viewport: edi
+ */
+void sub_688972(int screenX, int screenY, sint16 *x, sint16 *y, rct_viewport **viewport) {
+	int z;
+	rct_viewport *myViewport;
+	get_map_coordinates_from_pos(screenX, screenY, 0xFFFE, x, y, &z, NULL, &myViewport);
+	if (z == 0) {
+		*x = 0x8000;
+		return;
+	}
+
+	RCT2_GLOBAL(0x00F1AD34, uint16) = *x;
+	RCT2_GLOBAL(0x00F1AD36, uint16) = *y;
+	RCT2_GLOBAL(0x00F1AD38, uint16) = *x + 31;
+	RCT2_GLOBAL(0x00F1AD3A, uint16) = *y + 31;
+
+	rct_xy16 start_vp_pos = screen_coord_to_viewport_coord(myViewport, screenX, screenY);
+	rct_xy16 map_pos = { *x + 16, *y + 16 };
+
+	for (int i = 0; i < 5; i++) {
+		z = map_element_height(map_pos.x, map_pos.y);
+		map_pos = viewport_coord_to_map_coord(start_vp_pos.x, start_vp_pos.y, z);
+		map_pos.x = clamp(RCT2_GLOBAL(0x00F1AD34, uint16), map_pos.x, RCT2_GLOBAL(0x00F1AD38, uint16));
+		map_pos.y = clamp(RCT2_GLOBAL(0x00F1AD36, uint16), map_pos.y, RCT2_GLOBAL(0x00F1AD3A, uint16));
+	}
+
+	*x = map_pos.x;
+	*y = map_pos.y;
+
+	if (viewport != NULL) *viewport = myViewport;
+}
+
 /**
  *
  *  rct2: 0x0068958D
  */
-void screen_pos_to_map_pos(short *x, short *y, int *direction)
+void screen_pos_to_map_pos(sint16 *x, sint16 *y, int *direction)
 {
-	int eax, ebx, ecx, edx, esi, edi, ebp;
-	eax = *x;
-	ebx = *y;
-	RCT2_CALLFUNC_X(0x00688972, &eax, &ebx, &ecx, &edx, &esi, &edi, &ebp);
-	*x = eax & ~0x1F;
-	*y = ebx & ~0x1F;
+	sub_688972(*x, *y, x, y, NULL);
 	if (*x == 0x8000)
 		return;
 
@@ -1492,6 +1529,8 @@ void screen_pos_to_map_pos(short *x, short *y, int *direction)
 		}
 	}
 
+	*x = *x & ~0x1F;
+	*y = *y & ~0x1F;
 	if (direction != NULL) *direction = my_direction;
 }
 
diff --git a/src/interface/viewport.h b/src/interface/viewport.h
index b6e9d047f8..e53019738f 100644
--- a/src/interface/viewport.h
+++ b/src/interface/viewport.h
@@ -86,7 +86,8 @@ void sub_689174(sint16* x, sint16* y, sint16 *z);
 
 rct_xy16 screen_coord_to_viewport_coord(rct_viewport *viewport, uint16 x, uint16 y);
 rct_xy16 viewport_coord_to_map_coord(int x, int y, int z);
-void screen_pos_to_map_pos(short *x, short *y, int *direction);
+void sub_688972(int screenX, int screenY, sint16 *x, sint16 *y, rct_viewport **viewport);
+void screen_pos_to_map_pos(sint16 *x, sint16 *y, int *direction);
 
 void show_gridlines();
 void hide_gridlines();
diff --git a/src/interface/window.c b/src/interface/window.c
index ed5d376165..ea66ace556 100644
--- a/src/interface/window.c
+++ b/src/interface/window.c
@@ -1156,10 +1156,9 @@ void window_rotate_camera(rct_window *w)
 	sint16 y = (viewport->height >> 1) + viewport->y;
 	sint16 z;
 
-	int ecx, edx, esi, edi = (int)viewport, ebp;
 	//has something to do with checking if middle of the viewport is obstructed
-	RCT2_CALLFUNC_X(0x00688972, (int*)&x, (int*)&y, &ecx, &edx, &esi, &edi, &ebp);
-	rct_viewport *other = (rct_viewport*)edi;
+	rct_viewport *other;
+	sub_688972(x, y, &x, &y, &other);
 
 	// other != viewport probably triggers on viewports in ride or guest window?
 	// x is 0x8000 if middle of viewport is obstructed by another window?