CrystGLFW::Key

A CrystGLFW::Key (or Key, for the purposes of this guide) represents an individual key on the keyboard. Internally, Key is implemented as a Crystal Enum.

Key member names are derived from the names of the constants that represent them in the GLFW specification. The list of GLFW keys can be found here. Take the name of the constant, remove the "GLFWKEY" prefix and replace it with "Key::", and convert the rest of the key name to UpperCamelCase to get the member name. For example:

GLFW_KEY_A is represented in CrystGLFW as Key::A.
GLFW_KEY_LEFT_SHIFT is Key::LeftShift.
GLFW_KEY_EQUAL is :key::Equal.

And so on and so forth. A drawback of this approach is that key names that begin with a number must have that number spelled out:

GLFW_KEY_0 is represented in CrystGLFW as Key::Zero.
GLFW_Key_F1 is simply Key::F1, because it does not begin with a number.

Note: You'll want to check out this page from the GLFW docs if you're using a non-US keyboard and are confused by the results.

printable?

GLFW makes a distinction between "printable" keys and "non-printable" keys. You can see if a Key is printable by using the printable? method:

window.on_key do |event|
  puts event.key.printable? # => Bool
end

printable? returns true if the Key is printable, and returns false if it is not.

name

If a Key is "printable", then it has an internal name. You can retrieve this name using the name method:

window.on_key do |event|
  key = event.key
  puts key.name if key.printable?
end

If the Key is not printable, an exception will be raised.

Checking Keys

Because Key is an Enum, question methods are available for each possible value of a given Key:

window.on_key do |event|
  key = event.key
  if key.a?
    puts "key a was pressed"
  elsif key.b?
    puts "key b was pressed"
  elsif key.caps_lock?
    puts "caps lock was pressed"
  else
    puts "other key"
  end
end