Tutorial 03 Polling events

Tutorial 03 - Polling events

There are many ways to poll input events. The blocking function SDL.waitEvent will wait indefinitely until an event happens. The non-blocking function SDL.pollEvent will iterate over all ready events.

Except if you really need synchronous scenarios, SDL.pollEvent should be used.

Download full example: 03-events.tgz

Reading events

To read events, call SDL.pollEvent in a for loop. It returns a table with the information about the event. See Event for more information about the events.

while running do
    -- Iterate over all events, this function does not block.
    for e in SDL.pollEvent() do
        if e.type == SDL.event.Quit then
            running = false
        elseif e.type == SDL.event.KeyDown then
            print(string.format("key down: %d -> %s", e.keysym.sym, SDL.getKeyName(e.keysym.sym)))
        elseif e.type == SDL.event.MouseWheel then
            print(string.format("mouse wheel: %d, x=%d, y=%d", e.which, e.x, e.y))
        elseif e.type == SDL.event.MouseButtonDown then
            print(string.format("mouse button down: %d, x=%d, y=%d", e.button, e.x, e.y))
        elseif e.type == SDL.event.MouseMotion then
            print(string.format("mouse motion: x=%d, y=%d", e.x, e.y))
        end
    end
end

In this example we check the event's type and then log information about select event types.