Change selection grid to maintain relative horizontal position when switching rows (#329)

* Change selection grid to maintain relative horizontal position when switching rows

* clang-format

* Fixed joker selling index error

* Protect against division by 0 and removed redundant fixed point conversions.

source/game.c

@@ -3994,9 +3994,13 @@ static void jokers_sel_row_on_key_transit(SelectionGrid* selection_grid, Selecti
 
     if (key_hit(SELL_KEY))
     {
-        game_sell_joker(selection->x);
+        int sold_joker_idx = selection->x;
+
         // Move the selection away from the jokers so it doesn't point to an invalid place
+        // Do this before selling the joker so valid row sizes are used
         selection_grid_move_selection_vert(selection_grid, SCREEN_DOWN);
+
+        game_sell_joker(sold_joker_idx);
     }
 }
 

source/selection_grid.c

@@ -57,12 +57,15 @@ void selection_grid_move_selection_vert(SelectionGrid* selection_grid, int direc
         if (new_row_size <= 0)
             return;
 
-        if (selection.x >= new_row_size)
-        {
-            // TODO: Maintain relative horizontal position
-            // Clip selection to row size
-            new_selection.x = new_row_size - 1;
-        }
+        int old_row_size = selection_grid->rows[selection.y].get_size();
+
+        // Branchless set to 1 if 0 to avoid division by 0
+        old_row_size += (old_row_size == 0);
+
+        // Maintain relative horizontal position
+        // The operations are equivalent to fixed point if all the numbers were converted
+        new_selection.x = fx2int(selection.x * ((int2fx(new_row_size) / old_row_size)));
+
         if (selection.y >= 0 && selection.y < selection_grid->num_rows)
         {
             selection_grid->rows[selection.y]