McBopomofo allows users to input pheases with a different length of the
characters and Bopomofo readings, for example, users can input ∴ with ㄙㄨㄛˇ-ㄧˇ.
When the cursor if between ㄙㄨㄛˇ and ㄧˇ, the users have no clue where
the cursor exactly is. The tooltip is to tell the users the cursor is
now betwen ㄙㄨㄛˇ and ㄧˇ.
Since we use states manage the input flow in McBopomofo, implementing this function becomes easy. What I did is to create a new state, Associated Phrases state, and let the key handler to emit such a state just after emitting a Committing state.
When the input method controller is under Associated Phrase state, it shows the candidate window with a tooltip, and only accept candidate keys with the shift key. The key handler uses the characters without modifiers in an NSEvent object to find if there is any matching candidate label, so I added a new member "inputTextIgnoringModifiers" to KeyHandlerInput.
I use KeyValueBlobReader to read the associated phrases. I use the cin file from OpenVanilla project but removed the head and tail of the file to pass KeyValueBlobReader's validation.
zonble