GetAsyncKeyState vs. GetKeyState ?

[ThomasIngold]

Hello,

I'm coding a game and I use GetAsyncKeyState from the API to control my sprite... and it works btw :-)

What's the difference to GetKeyState ?

Is this a stupid question ? :-))

Thanks !
Tom

[Ungi]

Platform SDK: Windows User Interface
GetAsyncKeyState
The GetAsyncKeyState function determines whether a key is up or down at the time the function is called, and whether the key was pressed after a previous call to GetAsyncKeyState.

SHORT GetAsyncKeyState(
int vKey // virtual-key code
);Parameters
vKey
[in] Specifies one of 256 possible virtual-key codes. For more information, see Virtual-Key Codes.
Windows NT/2000 or later: You can use left- and right-distinguishing constants to specify certain keys. See the Remarks section for further information.

Return Values
If the function succeeds, the return value specifies whether the key was pressed since the last call to GetAsyncKeyState, and whether the key is currently up or down. If the most significant bit is set, the key is down, and if the least significant bit is set, the key was pressed after the previous call to GetAsyncKeyState. However, you should not rely on this last behavior; for more information, see the Remarks.

Windows NT/2000 or later: The return value is zero for the following cases:

The current desktop is not the active desktop
The foreground thread belongs to another process and the desktop does not allow the hook or the journal record.
Windows 95/98/Me: The return value is the global asynchronous key state for each virtual key. The system does not check which thread has the keyboard focus.

Windows 95: Windows 95 does not support the left- and right-distinguishing constants. If you call GetAsyncKeyState with these constants, the return value is zero.

Remarks
The GetAsyncKeyState function works with mouse buttons. However, it checks on the state of the physical mouse buttons, not on the logical mouse buttons that the physical buttons are mapped to. For example, the call GetAsyncKeyState(VK_LBUTTON) always returns the state of the left physical mouse button, regardless of whether it is mapped to the left or right logical mouse button. You can determine the system's current mapping of physical mouse buttons to logical mouse buttons by calling

GetSystemMetrics(SM_SWAPBUTTON) which returns TRUE if the mouse buttons have been swapped.

Although the least significant bit of the return value indicates whether the key has been pressed since the last query, due to the pre-emptive multitasking nature of Win32, another application can call GetAsyncKeyState and receive the "recently pressed" bit instead of your application. The behavior of the least significant bit of the return value is retained strictly for compatibility with 16-bit Windows applications (which are non-preemptive) and should not be relied upon.

You can use the virtual-key code constants VK_SHIFT, VK_CONTROL, and VK_MENU as values for the vKey parameter. This gives the state of the SHIFT, CTRL, or ALT keys without distinguishing between left and right.

Windows NT/2000 or later: You can use the following virtual-key code constants as values for vKey to distinguish between the left and right instances of those keys.

Code Meaning
VK_LSHIFT VK_RSHIFT
VK_LCONTROL VK_RCONTROL
VK_LMENU VK_RMENU


These left- and right-distinguishing constants are only available when you call the GetKeyboardState, SetKeyboardState, GetAsyncKeyState, GetKeyState, and MapVirtualKey functions.

Requirements
Windows NT/2000 or later: Requires Windows NT 3.1 or later.
Windows 95/98/Me: Requires Windows 95 or later.
Header: Declared in Winuser.h; include Windows.h.
Library: Use User32.lib.

See Also
Keyboard Input Overview, Keyboard Input Functions, GetKeyboardState, GetKeyState, GetSystemMetrics, MapVirtualKey, SetKeyboardState

Platform SDK Release: February 2001 Contact Platform SDK Order a Platform SDK CD Online



Requirements
Windows NT/2000 or later: Requires Windows NT 3.1 or later.
Windows 95/98/Me: Requires Windows 95 or later.
Header: Declared in Winuser.h; include Windows.h.
Library: Use User32.lib.
See Also
Keyboard Input Overview, Keyboard Input Functions, GetKeyboardState, GetKeyState, GetSystemMetrics, MapVirtualKey, SetKeyboardState

[Ungi]

GetKeyState
The GetKeyState function retrieves the status of the specified virtual key. The status specifies whether the key is up, down, or toggled (on, off—alternating each time the key is pressed).

SHORT GetKeyState(
int nVirtKey // virtual-key code
);Parameters
nVirtKey
[in] Specifies a virtual key. If the desired virtual key is a letter or digit (A through Z, a through z, or 0 through 9), nVirtKey must be set to the ASCII value of that character. For other keys, it must be a virtual-key code.
If a non-English keyboard layout is used, virtual keys with values in the range ASCII A through Z and 0 through 9 are used to specify most of the character keys. For example, for the German keyboard layout, the virtual key of value ASCII O (0x4F) refers to the "o" key, whereas VK_OEM_1 refers to the "o with umlaut" key.

Return Values
The return value specifies the status of the specified virtual key, as follows:

If the high-order bit is 1, the key is down; otherwise, it is up.
If the low-order bit is 1, the key is toggled. A key, such as the CAPS LOCK key, is toggled if it is turned on. The key is off and untoggled if the low-order bit is 0. A toggle key's indicator light (if any) on the keyboard will be on when the key is toggled, and off when the key is untoggled.
Remarks
The key status returned from this function changes as a thread reads key messages from its message queue. The status does not reflect the interrupt-level state associated with the hardware. Use the GetAsyncKeyState function to retrieve that information.

An application calls GetKeyState in response to a keyboard-input message. This function retrieves the state of the key when the input message was generated.

To retrieve state information for all the virtual keys, use the GetKeyboardState function.

An application can use the virtual-key code constants VK_SHIFT, VK_CONTROL, and VK_MENU as values for the nVirtKey parameter. This gives the status of the SHIFT, CTRL, or ALT keys without distinguishing between left and right. An application can also use the following virtual-key code constants as values for nVirtKey to distinguish between the left and right instances of those keys.

VK_LSHIFT

VK_RSHIFT

VK_LCONTROL

VK_RCONTROL

VK_LMENU

VK_RMENU

These left- and right-distinguishing constants are available to an application only through the GetKeyboardState, SetKeyboardState, GetAsyncKeyState, GetKeyState, and MapVirtualKey functions.

For an example, see Displaying Keyboard Input.

Requirements
Windows NT/2000 or later: Requires Windows NT 3.1 or later.
Windows 95/98/Me: Requires Windows 95 or later.
Header: Declared in Winuser.h; include Windows.h.
Library: Use User32.lib.

See Also
Keyboard Input Overview, Keyboard Input Functions, GetAsyncKeyState, GetKeyboardState, MapVirtualKey, SetKeyboardState

[ThomasIngold]

Thanks !

[Ungi]

Nice to help you!

[MGeorge]

Hello,

I would like to use GetKeyState to check whether the LButton is down at a particular point of time from my C# application. Can somebody help me how can I do it? When I tried this GetKeyState returns -127 and -128 if the mouse is down or up. But I dont know what does these values mean and how to find out whether the mouse is down.

Thanks in advance.....

[javajawa]

Come on...
You posted on a thread that was closed 5 years ago, in a forum irrelevant to you question, on a point that you could easily work out for yourself, or even just google, or (in fact) search these forums for the correct answer)

Write a short program which calls GetKeyState every second, and outputs the result to screen, file, listbox, whatever. Then, run it, and press the mouse button. When it's down, you'll get one number, when it's up, you'll get the other. Volia.