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Reasons not to use DirectInput for Keyboard Input

Posted by Evil Steve, 05 October 2007 · 1,220 views

I've got fed up searching through my past posts to copy and paste posts in reply to people using DirectInput for keyboard input. So I'll make an entry here, and then just link to it from other topics, and I'll edit this entry to add points.

Thanks to S1CA for keymaps, Input Method Editors and voice control points.

Reasons against using DirectInput for any form of keyboard input:
  • It creates a seperate thread to just read data from the keyboard using raw input (Which you can do yourself with Win32), meaning there's more overhead than just doing it yourself.
  • No support for keyboard repeat at the rate the user has set in the control pannel - you have to re-invent this yourself. Not too bad for game input, but a pain for GUI-style text input.
  • No support for capital letters and shifted characters - you have to detect caps lock / shift being held as well as your normal character (As Namethatnobodyelsetook was saying).
  • No support for caps lock on/off; it's handled by a higher layer than DirectInput, so if someone starts your game with caps lock on, it gets confused.
  • No support for keymaps other than US-English. A German user of your app pressing Z on their keyboard will show up in your app as a press of DIK_Y.
  • No support for Input Method Editors (commonly used for languages like Chinese).
  • No support for accessibility keyboards and things like voice control that require special drivers.

    And reasons not to use it for Mouse input:
  • No support for pointer ballistics (Pointer acceleration, more or less - but more complicated), which makes GUI style apps feel very strange
  • No support for getting mouse position in pixel coordinates (I.e. GetCursorPos() equivalent)

    And generally:
  • Much more code to get the same effect as Window Messages.
  • It's recommended that you DON'T use it by Microsoft; Link:
    Quote:
    Overall, using DirectInput offers no advantages when reading data from mouse or keyboard devices, and the use of DirectInput in these scenarios is discouraged.



    There's one occasion where it's acceptable to use DirectInput for mouse input, and that's if you need high DPI mouse input and you need to support pre-Win2k machines (Where raw input isn't available) - and that's supporting an OS that even Microsoft isn't supporting any longer. There are no other reasons you should ever use DI for mouse or keyboard input.

    EDIT: Added mouse input stuff.




  • Do you know a way to get movement ballistics just as when listening to WM_MOUSEMOVE events, but without the problem of the cursor being clamped to the screen borders? WM_MOUSEMOVE does not provide any information when the cursor is on the right edge of the screen and the mouse is moving to the right, for exemple. Does the ballistics have to be reimplemented from WM_INPUT messages?
    I believe most games reset the cursor to the center of the screen every frame if they want delta values and don't care about the absolute mouse position.
    You should add a remark that DirectInput still is the only viable choice for accessing ANY gamepad/controller beside the XBox 360 controller (which you should use XInput for).

    Edit: Typo
    I agree - although the point of this journal entry is reasons not to use it for keyboard or mouse input. There's no problem with using DirectInput for other input devices.
    Hi Evil Seve.
    this would have been usefull about 2 weeks ago, some guy thought that quating MSDN(while i fergot the link to it) was rubbish and random advice.

    MSDN says your link has been moved, here is the direct link to it:
    http://msdn.microsoft.com/en-us/library/ee418864.aspx
    :)
    PARTNERS