Keyboard Input

The SDL2InputSystem broadcasts keyboard events, which can be listened to and parsed to handle keyboard input.

Subscribing to Key Events

There are two keyboard events that can be subscribed to, MESSAGE_KEY_DOWN_EVENT and MESSAGE_KEY_UP_EVENT.

#include "standard/sdl2_input/sdl2_input_system.hpp"
...
YourSystem::YourSystem(JamJar::MessageBus *messageBus) : JamJar::System(messageBus) {
    this->messageBus->Subscribe(this, JamJar::Standard::SDL2InputSystem::MESSAGE_KEY_DOWN_EVENT);
    this->messageBus->Subscribe(this, JamJar::Standard::SDL2InputSystem::MESSAGE_KEY_UP_EVENT);
}

Parsing Key Events

Each key event message has a payload which is of type SDL2KeyEvent which contains some useful quick access information, alongside the raw SDL_Event that gives full advanced key event information.

The quick access information in the SDL2KeyEvent is:

• Key name as a character array.
• The key event type, expressed as an SDL2KeyEventType enum.
• If the key event is a repeat (holding down a key will generate multiple key down events, the duplicates are marked as repeat, this is useful for handling user text input).

See the SDL2 documentation for a full reference of the raw SDL_Event.

#include "standard/sdl2_input/sdl2_input_system.hpp"
...
void YourSystem::OnMessage(JamJar::Message *message) {
    System::OnMessage(message);
    switch (message->type) {
    case JamJar::Standard::SDL2InputSystem::MESSAGE_KEY_DOWN_EVENT: {
        auto *eventMessage = static_cast<JamJar::MessagePayload<JamJar::Standard::SDL2KeyEvent> *>(message);
        auto event = eventMessage->payload;
        if (event.repeat) {
            // Ignore repeat keypresses
            break;
        }
        std::cout << "listener got key down: " << event.key << std::endl;
        break;
    }
    case JamJar::Standard::SDL2InputSystem::MESSAGE_KEY_UP_EVENT: {
        auto *eventMessage = static_cast<JamJar::MessagePayload<JamJar::Standard::SDL2KeyEvent> *>(message);
        auto event = eventMessage->payload;
        if (event.repeat) {
            break;
        }
        std::cout << "listener got key up: " << event.key << std::endl;
        break;
    }
    }
}