4 button RS touchscreen

mon = peripheral.find("monitor")

a = false
b = false
c = false
d = false

function drawButtons()
x,y = mon.getSize()
mon.clear()
mon.setTextColor(colors.black)
if a == true then
   mon.setBackgroundColor(colors.white)
else
   mon.setBackgroundColor(colors.gray)
end
for yc = 1, y/2+1 do
    for xc = 1, x/2+1 do
        mon.setCursorPos(xc,yc)
        mon.write(" ")
    end
end
mon.setCursorPos(x/4+1, y/4)
mon.write("1")
if b == true then
   mon.setBackgroundColor(colors.white)
else
   mon.setBackgroundColor(colors.gray)
end
for yc = 1, y/2+1 do
    for xc = x/2+1, x do
        mon.setCursorPos(xc,yc)
        mon.write(" ")
    end
end
mon.setCursorPos(x/4*3+1, y/4)
mon.write("2")
if c == true then
   mon.setBackgroundColor(colors.white)
else
   mon.setBackgroundColor(colors.gray)
end
for yc = y/2+1, y do
    for xc = 1, x/2+1 do
        mon.setCursorPos(xc,yc)
        mon.write(" ")
    end
end
mon.setCursorPos(x/4+1, y/4*3)
mon.write("3")
if d == true then
   mon.setBackgroundColor(colors.white)
else
   mon.setBackgroundColor(colors.gray)
end
for yc = y/2+1, y do
    for xc = x/2+1, x do
        mon.setCursorPos(xc,yc)
        mon.write(" ")
    end
end
mon.setCursorPos(x/4*3+1, y/4*3)
mon.write("4")
end


while true do
    drawButtons()
    event, param1, param2, param3 = os.pullEvent("monitor_touch")
    if param2 < x/2 and param3 < y/2 then
        if a == false then
            rs.setOutput("front", true)
            a = true
        else
            rs.setOutput("front", false)
            a = false
        end
    elseif param2 > x/2 and param3 < y/2 then
        if b == false then
            rs.setOutput("right", true)
            b = true
        else
            rs.setOutput("right", false)
            b = false
        end
    elseif param2 < x/2 and param3 > y/2 then
        if c == false then
            rs.setOutput("back", true)
            c = true
        else
            rs.setOutput("back", false)
            c = false
        end
    elseif param2 > x/2 and param3 > y/2 then
        if d == false then
            rs.setOutput("left", true)
            d = true
        else
            rs.setOutput("left", false)
            d = false
        end
    end
end