Difference between revisions of "Raw key events"

Latest revision as of 22:05, 21 December 2012

The built-in os has a function to read incoming keystrokes. But it also implements the functions to move the cursor while typing. This is not always a desired feature; imagine a case in which you want to make a menu with a controllable cursor around the menu entries. The current read() function won't let you.

Detecting keystrokes

In case I made you think the OS sucks, it doesn't (all the time). Because this OS is not Windows, we can access lower-level functions, such as os.pullEvent(). And that's the one that we're going to use:

function rawread()
    bRead = true
    while(bRead) do
        local sEvent, param = os.pullEvent("key")
        if(sEvent == "key") then
            break
        end
    end
end

This function waits for any key, then exits.

Figuring out the key

We can detect any key, but not which key. To find it out, we have to add some further logic to the code:

function rawread()
    while true do
        local sEvent, param = os.pullEvent("key")
        if sEvent == "key" then
            if param == 28 then
                print("Enter detected")
                break
            end
        end
    end
end

This function waits for the Enter key to be pressed. If so, it writes "Enter detected" to the screen and exits.

Key scan codes

Click for a larger copy of this image - contains keys and their event numbers.