Behold the Table Driven Text Service, Part 3 (Where do keystrokes come in?)

by Michael S. Kaplan, published on 2008/01/24 10:16 -05:00, original URI: http://blogs.msdn.com/b/michkap/archive/2008/01/24/7180212.aspx

Prior posts in the series:

• 0 (You have to start somewhere)
• 1 (Starting with a dictionary simple in every way)
• 2 (Three ways to convert!)

Now I did not start this at the beginning, I kind of picked it up in the middle. Here is some info that is nice to know very near to the beginning, though....

Here are the pre-defined keystrokes and how they behave in the Candidate Window.

Note that they are Virtual Key (VK) based. I will get to the consequences of that in a moment.

While composing:

Virtual Key	Function
VK_LEFT	Move caret to left in composition char If we have the Incremental Candidate List, then cancel composition.
VK_RIGHT	Move caret to right in composition char If we have the Incremental Candidate List, then cancel composition
VK_RETURN	Finalize composition char
VK_ESCAPE	Cancel composition char
VK_BACK	Delete one composition char
VK_SPACE	Convert composition char
VK_UP	If we have the Incremental Candidate List, then move candidate selection to up
VK_DOWN	If we have the Incremental Candidate List, then move candidate selection to down
VK_PRIOR	If we have the Incremental Candidate List, then move candidate selection to prior
VK_NEXT	If we have the Incremental Candidate List, then move candidate selection to next
VK_HOME	If we have the Incremental Candidate List, then move candidate selection to home
VK_END	If we have the Incremental Candidate List, then move candidate selection to end

And then in the Candidate/Phrase Window:

Virtual Key	Function
VK_UP	Move candidate selection to up
VK_DOWN	Move candidate selection to down
VK_PRIOR	Move candidate selection to prior
VK_NEXT	Move candidate selection to next
VK_HOME	Move candidate selection to home
VK_END	Move candidate selection to end
VK_RETURN	Finalize candidate list
VK_ESCAPE	Cancel candidate list
VK_BACK	Cancel candidate list
VK_1 - VK_9	Select list item for corresponding number, one through nine

Now each text file has a section it in that is key to how every other character is handled. Here is what it looks like in our MSDN_TableTextService_Explicit.txt file:

[Keystroke.Composition]
VK_1,          0  = INPUT        // 1
VK_2,          0  = INPUT        // 2
VK_3,          0  = INPUT        // 3
VK_4,          0  = INPUT        // 4
VK_5,          0  = INPUT        // 5
VK_6,          0  = INPUT        // 6
VK_7,          0  = INPUT        // 7
VK_8,          0  = INPUT        // 8
VK_9,          0  = INPUT        // 9

Now as that list might or might not seem to indicate, all other keys just pass right through to the underlying keyboard that sits underneath the Tabld Driven TIP.

But adding a VK_* value to this list will cause keystrokes from that VK to be processed by the Table Driven Text Service -- and if those letters never appear in the [Text] section then those keystrokes will be eaten.

Now there are a few more advanced features, which I'll discuss soon.

And there is the interaction between the predefined keys and the ones you define in the file -- basically the rule is easy and simple for the DLL -- it always wins. Which means if you define something then it will alwys pay attention to you unless it has its own override (hih is why VK_1 - VK_9 have that weird behavior where as soon as you have a candidate list then if it is numbered then the candidate item selection takes prioirty over the actual input -- which leads to VERY confusing behavior.

I'll discuss this more soon, as well. :-)

At this point, you may be wondering about two more things -- the meaning of the INPUT keyword here, and the meaning of the number 0. The fact that every single text file on Vista includes these very same entries is just a special bonus to people trying to figure out the meaning without assistance or documentation....

If you are one of those people then you can take comfort in the fact that I was too, so I'll be getting to this very soon, in an upcoming blog in this series. :-)

Coming up soon, maybe next -- some really explicit information about the [TEXT] section, and more information on some of the configuration sections....

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