A Cinder application can respond to key events through several callbacks.
The available callbacks that get called by keyboard interaction are listed in the following table:
Method |
Usage |
---|---|
This is called when the user first presses a key and called repeatedly if a key is kept pressed. | |
This is called when a key is released. |
Both these methods receive a ci::app::KeyEvent
object as a parameter with information about the event such as the key code being pressed or if any special key (such as Shift or control) is being pressed.
It is not mandatory to implement all of the preceding key event handlers; you can implement only the ones that your application requires.
Implement the necessary event handlers according to what key events you need to respond to. For example, to create an application that responds to both key down and key up events, you must declare the following methods:
void keyDown( KeyEvent event ); void keyUp( KeyEvent event );
The ci::app::KeyEvent
parameter contains information about the key event.
We will learn how to work with the ci::app::KeyEvent
class to learn how to understand key events. Perform the following steps to do so:
char character = event.getChar();
getCode
method that retrieves an int
value that can be mapped to a character table in the ci::app::KeyEvent
class. To test, for example, if the key event was triggered by the Esc key you can type in the following line of code:bool escPressed = event.getCode() == KeyEvent::KEY_ESCAPE;
escPressed
will be true
if the escape key triggered the event, or false
otherwise.
ci::app::KeyEvent
parameter also has information about modifier keys that were pressed during the event. The isShiftDown
method returns true
if the Shift key was pressed, isAltDown
returns true
if the Alt key was pressed, isControlDown
returns true
if the control key was pressed, isMetaDown
returns true
if the Windows key was pressed on Windows or the command key was pressed on OS X, and isAccelDown
returns true
if the Ctrl key was pressed on Windows or the command key was pressed on OS X.A Cinder application responds internally to the system's native key events. When receiving a native key event, it creates a ci::app::KeyEvent
object based on the native information and calls the correspondent callback on our application's class.
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