Jumping instead of Walking :(

i am trying to modify a code that works with keyboard to make it work with the mouse. The problem is when i click with the mouse it jumps directly to the new Y position (WorldY) instead of walking to get the new position.

the original code is the following:

        ; Going Down
        Case 2
             OldY = WorldY
             WorldY = WorldY + Distance 
             If WorldY > Map_Height * TileHeight - TileHeight
                WorldY = Map_Height * TileHeight - TileHeight
             EndIf

is there an example of replacing arrow keys with the mouse + left click to walk?

i was all week end trying to make it work, but it didn't :'(