Change Terrain type at unit if true in jass:)

function Trig_Terrain_Change_at_u_Actions takes nothing returns nothing
 local real x
 local real y
 local integer i = 1
    loop
        exitwhen i > 3
        set x = GetUnitX(udg_Slider[i])
        set y = GetUnitY(udg_Slider[i])
        if udg_SuperSlide == true then
        call SetTerrainTypeBJ(x, y, 'Lgrd', -1, 1, 1 )
        endif
    set i = (i+1)
    endloop
endfunction

//===========================================================================
function InitTrig_Terrain_Change_at_u takes nothing returns nothing
    set gg_trg_Terrain_Change_at_u = CreateTrigger(  )
    call TriggerRegisterTimerEventPeriodic( gg_trg_Terrain_Change_at_u, 0.03 )
    call TriggerAddAction( gg_trg_Terrain_Change_at_u, function Trig_Terrain_Change_at_u_Actions )
endfunction