mouse_event

The mouse_event function synthesizes mouse motion and button clicks.

VOID mouse_event(

DWORD dwFlags,	// flags specifying various motion/click variants
DWORD dx,	// horizontal mouse position or position change
DWORD dy,	// vertical mouse position or position change
DWORD dwData,	// amount of wheel movement
DWORD dwExtraInfo	// 32 bits of application-defined information
);

Parameters

dwFlags

A set of flag bits that specify various aspects of mouse motion and button clicking. The bits in this parameter can be any reasonable combination of the following values:

Value	Meaning
MOUSEEVENTF_ABSOLUTE	Specifies that the dx and dy parameters contain normalized absolute coordinates. If not set, those parameters contain relative data: the change in position since the last reported position. This flag can be set, or not set, regardless of what kind of mouse or mouse-like device, if any, is connected to the system. For further information about relative mouse motion, see the following Remarks section.
MOUSEEVENTF_MOVE	Specifies that movement occurred.
MOUSEEVENTF_LEFTDOWN	Specifies that the left button changed to down.
MOUSEEVENTF_LEFTUP	Specifies that the left button changed to up.
MOUSEEVENTF_RIGHTDOWN	Specifies that the right button changed to down.
MOUSEEVENTF_RIGHTUP	Specifies that the right button changed to up.
MOUSEEVENTF_MIDDLEDOWN	Specifies that the middle button changed to down.
MOUSEEVENTF_MIDDLEUP	Specifies that the middle button changed to up.
MOUSEEVENTF_WHEEL	Windows NT only: Specifies that the wheel has been moved, if the mouse has a wheel. The amount of movement is given in dwData

The flag bits that specify mouse button status are set to indicate changes in status, not ongoing conditions. For example, if the left mouse button is pressed and held down, MOUSEEVENTF_LEFTDOWN is set when the left button is first pressed, but not for subsequent motions. Similarly, MOUSEEVENTF_LEFTUP is set only when the button is first released.

dx

Specifies the mouse's absolute position along the x-axis or its amount of motion since the last mouse event was generated, depending on the setting of MOUSEEVENTF_ABSOLUTE. Absolute data is given as the mouse's actual x-coordinate; relative data is given as the number of mickeys moved.

dy

Specifies the mouse's absolute position along the y-axis or its amount of motion since the last mouse event was generated, depending on the setting of MOUSEEVENTF_ABSOLUTE. Absolute data is given as the mouse's actual y-coordinate; relative data is given as the number of mickeys moved.

dwData

If dwFlags is MOUSEEVENTF_WHEEL, then dwData specifies the amount of wheel movement. A positive value indicates that the wheel was rotated forward, away from the user; a negative value indicates that the wheel was rotated backward, toward the user. One wheel click is defined as WHEEL_DELTA, which is 120.

If dwFlags is not MOUSEEVENTF_WHEEL, then dwData should be zero.

dwExtraInfo

Specifies an additional 32-bit value associated with the mouse event. An application calls GetMessageExtraInfo to obtain this extra information.

Return Values

This function has no return value.

Remarks

If the mouse has moved, indicated by MOUSEEVENTF_MOVE being set, dx and dy hold information about that motion. The information is given as absolute or relative integer values.

If MOUSEEVENTF_ABSOLUTE value is specified, dx and dy contain normalized absolute coordinates between 0 and 65,535. The event procedure maps these coordinates onto the display surface. Coordinate (0,0) maps onto the upper-left corner of the display surface, (65535,65535) maps onto the lower-right corner.

If the MOUSEEVENTF_ABSOLUTE value is not specified, dx and dy specify relative motions from when the last mouse event was generated (the last reported position). Positive values mean the mouse moved right (or down); negative values mean the mouse moved left (or up).

Relative mouse motion is subject to the effects of the mouse speed and the two mouse threshold values. In Windows NT, an end user sets these three values with the Mouse Tracking Speed slider of Control Panel's Mouse option; in Windows 95, an end user sets them with the Pointer Speed slider of the Control Panel's Mouse property sheet. An application obtains and sets these values with the SystemParametersInfo function.

The operating system applies two tests to the specified relative mouse motion. If the specified distance along either the x or y axis is greater than the first mouse threshold value, and the mouse speed is not zero, the operating system doubles the distance. If the specified distance along either the x or y axis is greater than the second mouse threshold value, and the mouse speed is equal to two, the operating system doubles the distance that resulted from applying the first threshold test. It is thus possible for the operating system to multiply relatively-specified mouse motion along the x or y axis by up to four times.

The mouse_event function is used to synthesize mouse events by applications that need to do so. It is also used by applications that need to obtain more information from the mouse than its position and button state. For example, if a tablet manufacturer wants to pass pen-based information to its own applications, it can write a dynamic-link library (DLL) that communicates directly to the tablet hardware, obtains the extra information, and saves it in a queue. The DLL then calls mouse_event with the standard button and x/y position data, along with, in the dwExtraInfo parameter, some pointer or index to the queued extra information. When the application needs the extra information, it calls the DLL with the pointer or index stored in dwExtraInfo, and the DLL returns the extra information.

See Also

GetMessageExtraInfo, SystemParametersInfo

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