Add Text Input/Editing to EventHandler

[ldicker83]

The EventHandler currently has no notion of text input. This required a KeyTranslator object that would take basic keyboard events and translate them into ASCII characters.

SDL2.0 introduced text editing/input events that handle this far better than the KeyTranslator. It stands to reason then that EventHandler should adopt similar functionality.

Implementation Details

The EventHandler will need to add functions to enable and disable text input/editing and poll the current input editing state:

void EventHandler::textInputMode(bool); // true to turn on, false to turn off.
bool EventHandler::textInputMode(); // Queries the input state

Event signal:

NAS2D::Signals::Signal1<std::string> TextInputEventCallback;

Potential for Defects

The option to use a std::string by value vs. by reference here is intended to prevent inevitable mistakes. While passing by reference would work normally for typical uses (by the time the local string object is destroyed the signal observer will have already copied the string) and would certainly be more efficient, there will be times when someone will attempt to maintain a reference to the std::string either as a reference or as a pointer. In these cases the application will eventually segfault because as soon as the Signal1<std::string&>::Emit() function returns the memory for the std::stringwill be automatically deallocated resulting in dangling pointers/references.

While this is generally inefficient due to the number of c'tors and copy operations, it ensures correct behavior. Additionally, reasonably good optimizing compilers can eliminate a lot of the overhead in release builds.

[ldicker83]

This was surprisingly simple to implement and is also surprisingly effective. It's definitely a lot more effective than the previous method.