gistfile1.lua

-- OpenPeripheral terminal glasses demo
-- by boq

local p = peripheral.wrap("back")

if p == nil then
    print("Peripheral not found")
    return
end

p.clear()

-- helper function and constants
function pack(...)
    return {...}
end

FORMAT_CHAR = "\194\167"
FORMAT_BOLD = FORMAT_CHAR .. 'l'

-- NOTE
-- this program works with multiple users (i.e. multiple players attached to same terminal) so it may be more complicated then single user variant
-- if it's not needed, programs may as well operate only on global surface
local players = {}

local attachedCount = 0
local capturedCount = 0

-- initialize global display surface
local labelPlayers = p.addText(-1, 0, "Player count: 0/0");
labelPlayers.setScreenAnchor("right", "top") -- screen origin (0,0) for this object will be in top right corner
labelPlayers.setObjectAnchor("right", "bottom") -- "center" of object will be on bottom right corner
labelPlayers.setRotation(-90) -- object will be rotated by 90 degrees counter-clockwise around object anchor (bottom right corner)

local function initializePlayer(name, uuid)
    local playerData = { name = name, uuid = uuid}

    -- now we can use private surface, visible only to owner player
    playerData.surface = p.getSurfaceByUUID(playerData.uuid)
    labelPlayer = playerData.surface.addText(0, 0, "Hello " .. playerData.name)
    labelPlayer.setAlignment("middle","top") -- identical as 'labelPlayer.setScreenAnchor("middle","top") labelPlayer.setObjectAnchor("middle","top")'

    -- Minecraft color codes are interpreted (http://minecraft.gamepedia.com/Formatting_codes) - but since Lua does not support Unicode, you need to use "\194\167" instead of "\x00A7"
    playerData.labelWaiting = playerData.surface.addText(0, 0, FORMAT_BOLD .. "CAPTURE MODE: OFF", 0xFF0000)
    playerData.labelWaiting.setAlignment("right", "bottom")

    -- add to global list
    -- general hint: it's always safer to use UUID instead of names!
    players[playerData.uuid] = playerData
end

local function changeCounter(deltaAttached, deltaCaptured)
    attachedCount = attachedCount + deltaAttached
    capturedCount = capturedCount + deltaCaptured
    labelPlayers.setText("Player count: " .. attachedCount .. "/" .. capturedCount)
end

-- initialize already attached players
for _, user in pairs(p.getUsers()) do
    initializePlayer(user.name, user.uuid)
    changeCounter(1, 0)
end

local timerCallbacks = {}

p.sync() -- this operation is needed to make changes visible to player
-- classic event loop
while true do
    evt = pack(os.pullEvent())
    -- full list of glasses events: https://gist.github.com/boq/9a098b89ee102cbf1b2b
    print(evt[1])
    --  easy break condition - it's just ComputerCraft event
    if evt[1] == "key" then
        break -- exit loop
    -- player started wearing glasses
    elseif evt[1] == "glasses_attach" then
        local name = evt[3]
        local uuid = evt[4]
        initializePlayer(name, uuid)
        changeCounter(1, 0)
    -- player logged out or took off glasses
    elseif evt[1] == "glasses_detach" then
        -- components on private surface are automatically cleared when player removes glasses
        local playerUuid = evt[4]
        players[playerUuid] = nil
        changeCounter(-1,0)
    -- player used wireless keyboard - computer will now start getting keyboard and mouse events
    elseif evt[1] == "glasses_capture" then
        changeCounter(0, 1)
        local playerUuid = evt[4]
        local playerData = players[playerUuid]

        if playerData then
            local surface = playerData.surface
            playerData.labelWaiting.setText(FORMAT_BOLD .. "CAPTURE MODE: ON")
            playerData.labelWaiting.setColor(0x00FF00)

            -- middle boxes - will be used as bottons and to present click position
            local function createBox(color)
                local box = surface.addBox(0,0, 25, 25, color)
                box.setScreenAnchor("middle","middle")
                box.setUserdata(color) -- userdata is variable that can be used to store anything (no type or content restrictions, except for functions). It's also not synchronized to clients
                return box
            end

            createBox(0xFF0000).setObjectAnchor("left", "top")
            createBox(0x00FF00).setObjectAnchor("right", "top")
            createBox(0x0000FF).setObjectAnchor("right", "bottom")
            createBox(0xFFFFFF).setObjectAnchor("left", "bottom")

            -- horizontal progress bar
            surface.addBox(0,20, 100, 5, 0x000000).setAlignment("middle","top")

            -- vertical progress bar
            surface.addBox(0,0, 5, 100, 0x000000).setAlignment("right","middle")

            playerData.horizontalMarker = surface.addBox(0, 20, 5, 5, 0xFFFFFF)
            playerData.horizontalMarker.setAlignment("middle","top")

            playerData.verticalMarker = surface.addBox(0, 0, 5, 5, 0xFFFFFF)
            playerData.verticalMarker.setAlignment("right","middle")

            -- pseudo-console stuff
            playerData.textInput = surface.addText(0,0,">", 0x00FF00)
            playerData.textInput.setScreenAnchor("left", "middle")
            playerData.textInput.setObjectAnchor("left", "bottom")

            playerData.textOutput = surface.addText(0,0,"", 0x0000FF)
            playerData.textOutput.setScreenAnchor("left", "middle")
            playerData.textOutput.setObjectAnchor("left", "top")
            playerData.textOutput.setVisible(false)

            -- mouse button indicator
            surface.addBox(10, 10, 19, 9, 0xAAAAAA).setObjectAnchor("middle","top") -- button indicator background

            playerData.mouseButtons = {}

            local function createMouseButton(deltaX)
                local button = surface.addBox(10 + deltaX, 12, 5, 5, 0xFF0000)
                button.setZ(5) -- move it over box (default Z == 0)
                button.setVisible(false)
                button.setObjectAnchor("middle","top")
                return button
            end

            -- mouse and keyboard codes are same as LWJGL, see http://minecraft.gamepedia.com/Key_codes

            playerData.mouseButtons[0] = createMouseButton(-5) -- left button
            playerData.mouseButtons[1] = createMouseButton(5) -- right button
            playerData.mouseButtons[2] = createMouseButton(0) -- middle button
        end
    -- player exited from keyboard GUI
    elseif evt[1] == "glasses_release" then
        changeCounter(0, -1)
        local playerUuid = evt[4]
        local playerData = players[playerUuid]

        if playerData then
            -- recreate display to initial state
            playerData.surface.clear()
            initializePlayer(playerData.name, playerData.uuid)
        end
    -- player pressed mouse button anywhere in GUI
    elseif evt[1] == "glasses_mouse_down" then
        local playerUuid = evt[4]
        local playerData = players[playerUuid]

        if playerData then
            local buttonId = evt[5]
            -- changing visibility is faster than recreating and removing element every time
            local button = playerData.mouseButtons[buttonId]
            if button then
                button.setVisible(true)
            end
        end
    -- player released mouse button anywhere in GUI
    elseif evt[1] == "glasses_mouse_up" then
        local playerUuid = evt[4]
        local playerData = players[playerUuid]

        local buttonId = evt[5]

        if playerData then
            button = playerData.mouseButtons[buttonId]
            if button then
                button.setVisible(false)
            end
        end

    -- player clicked on component (if you got this event, then you won't get glasses_mouse_down. Same for glasses_component_mouse_up and glasses_mouse_up)
    elseif evt[1] == "glasses_component_mouse_down" then
        local isPrivate = evt[6]
        if isPrivate then
            local playerUuid = evt[4]
            local playerData = players[playerUuid]

            if playerData then
                local objectId = evt[5]
                local component = playerData.surface.getObjectById(objectId)
                local userdata = component.getUserdata()
                if userdata then -- only rectangles in middle have that value filled
                    -- capture control is special object used to control few properties of keyboard GUI
                    local capture = p.getCaptureControl(playerUuid)
                    capture.setBackground(userdata)
                    playerData.horizontalMarker.setColor(userdata)
                    playerData.verticalMarker.setColor(userdata)
                end

                -- click position is given in pixels from top left component corner
                local clickX = evt[7]
                local clickY = evt[8]

                -- -0.5, since anchor is in middle of screen
                playerData.horizontalMarker.setX((clickX / 25.0 - 0.5) * 100)
                playerData.verticalMarker.setY((clickY / 25.0 - 0.5) * 100)
            end
        end
    elseif evt[1] == "glasses_key_down" then
        local playerUuid = evt[4]
        local playerData = players[playerUuid]

        if playerData then
            local code = evt[5] -- control code, see http://minecraft.gamepedia.com/Key_codes for keymap
            local char = evt[6] -- may be 0 for some control characters

            local input = playerData.textInput
            local contents = input.getText()
            if code == 14 then -- backspace
                if contents:len() > 1 then
                    input.setText(contents:sub(0, -2))
                end
            elseif code == 28 then -- enter
                input.setText(">")

                local function setOutput(text, color)
                    playerData.textOutput.setText(text)
                    playerData.textOutput.setColor(color)
                    playerData.textOutput.setVisible(true)
                    local timerId = os.startTimer(1)
                    timerCallbacks[timerId] = function ()
                        playerData.textOutput.setVisible(false)
                    end
                end

                -- alternative to writing tons of ifs. Normally would be initialized once before main loop, but this is demo/semi-tutorial
                local commands = {}

                function commands.hello(playerData)
                    setOutput("Hi!", 0xFFFF00)
                end

                function commands.exit(playerData)
                    -- manually exit keyboard GUI. Player can do it itself by using escape button (same as normal Minecraft GUIs)
                    p.getCaptureControl(playerData.uuid).stopCapturing()
                end

                -- sorry, couldn't resist
                local function createColorCommand(color)
                    return function(playerData)
                        playerData.textInput.setColor(color)
                        setOutput("OK", color)
                    end
                end

                commands.red = createColorCommand(0xFF0000)
                commands.green = createColorCommand(0x00FF00)
                commands.blue = createColorCommand(0x0000FF)

                command = contents:sub(2, -1)
                commandSub = commands[command] -- skip console prompt

                if commandSub then
                    commandSub(playerData)
                else
                    setOutput("invalid command: " .. command, 0xFF0000)
                end

            elseif string.byte(char) >= 0x20 then -- skip unprintable control chars
                input.setText(contents .. char)
            end
        end
    elseif evt[1] == "timer" then
        local timerId = evt[2]
        callback = timerCallbacks[timerId]
        if callback then callback() end
        timerCallbacks[timerId] = nil
    end

    -- sync() shouldn't be called often
    -- if called without changes, nothing will happen
    -- this method is synchronized - i.e. it can be executed only once per game tick (1/20 s). Other instructions don't have that limit
    p.sync()
end

What version of OP-A are you using for this?