Keyboard Events
Learn how to handle keyboard events with our own callbacks
Source Code
- The code for this tutorial can be found on Github : Learn SFML – Keyboard Event Scene
SFML Keyboard Events
Every time you play with your keyboard buttons, SFML will generate three types of Events
- sf::Event::KeyPressed : Emitted when you press a button
- sf::Event::KeyReleased : Emitted when you remove your finger from the button
- sf::TextEntered : Emitted when a valid Unicode character is detected
What is a Unicode character ? it’s any character representing a letter or a sign (punctuation, etc.) You can find a list here. The events KeyPressed and TextEntered seem similar but are actually different. For example, pressing SHIFT + A will generate the Unicode character uppercase “A”, so SFML will generate one event TextEntered but two events KeyPressed because two keys have been pressed SHIFT and A.
- TextEntered is used when you write a text, for example writing the name of your hero or a password in your game
- KeyPressed and KeyReleased are used for actual actions in your game, like running, jumping, etc.
void handleEvent(const sf::Event& event)
{
if(event.type == sf::Event::KeyPressed)
{
sf::Keyboard::Key key = event.key.code; //key name : A, B, SpaceBar etc.
bool alt = event.key.alt;
bool control = event.key.control;
bool shift = event.key.shift;
bool system = event.key.system;
if(key == sf::Keyboard::A)
{
nero_log("Pressing on A");
}
if(key == sf::Keyboard::A && control)
{
nero_log("Pressing on CTRL + A");
}
}
else if(event.type == sf::Event::KeyReleased)
{
sf::Keyboard::Key key = event.key.code; //key name : A, B, SpaceBar etc.
bool alt = event.key.alt;
bool control = event.key.control;
bool shift = event.key.shift;
bool system = event.key.system;
if(key == sf::Keyboard::A)
{
nero_log("Releasing A");
}
if(key == sf::Keyboard::A && control)
{
nero_log("Releasing CTRL + A");
}
}
if (event.type == sf::Event::TextEntered)
{
sf::Uint32 unicode = event.text.unicode;
//Make sure the unicode character is valid (value should be below 128)
if (event.text.unicode < 128)
{
std::string text = std::string(1, (static_cast(event.text.unicode)));
nero_log(text);
}
}
}Keyboard Events Callbacks
Now that you know how to use those 3 events, let’s improve our code by implementing our own callbacks. Instead of handling the Keyboard Events inside the Event Loop, we’ll use the two callbacks below
- void onKeyboardButton(const sf::Keyboard::Key& key, const bool& isPressed, const ModifierKey& modifier)
- void onTextEntered(const std::string& c)
The structure ModifierKey is used to store the four modifier keys states in one variable.
struct ModifierKey
{
bool alt = false;
bool control = false;
bool shift = false;
bool system = false;
};
void onKeyboardButton(const sf::Keyboard::Key& key, const bool& isPressed, const ModifierKey& modifier)
{
//do something
//key : name of the key (A, B, SpaceBar etc.)
//isPressed : is the keyPressed or released ?
//modifier : the state of the modifier keys (CTRL, ATL, SHIFT, SYSTEM)
}
void onTextEntered(const std::string& c)
{
//do something
// hero_name += c;
}The code below shows our new improved handleEvent(event) method, pretty isn’t it !?
void handleEvent(const sf::Event& event)
{
if(event.type == sf::Event::KeyPressed)
{
ModifierKey modifier;
modifier.alt = event.key.alt;
modifier.control = event.key.control;
modifier.shift = event.key.shift;
modifier.system = event.key.system;
onKeyboardButton(event.key.code, true, modifier);
}
else if(event.type == sf::Event::KeyReleased)
{
ModifierKey modifier;
modifier.alt = event.key.alt;
modifier.control = event.key.control;
modifier.shift = event.key.shift;
modifier.system = event.key.system;
onKeyboardButton(event.key.code, false, modifier);
}
if (event.type == sf::Event::TextEntered)
{
if (event.text.unicode < 128)
{
onTextEntered(std::string(1, (static_cast(event.text.unicode))));
}
}
}