How Can SetWindowPos Accurately Position Windows Across Multiple Monitors?

Mastering SetWindowPos for Multi-Monitor Window Placement

This article addresses the challenges of using SetWindowPos to position windows accurately across multiple monitors. We'll detail how to precisely place windows on specific screens using SetWindowPos in conjunction with other Windows API functions.

Understanding Screen Geometry and the Virtual Desktop

In Windows, the primary monitor's top-left corner is (0, 0). Monitors to the left have negative X coordinates, those to the right have positive X coordinates. The virtual desktop encompasses all connected monitors.

Retrieving Monitor Information

Obtain a monitor's handle using GetHashCode() (for a Screen object) or Win32 functions like MonitorFromWindow, MonitorFromPoint, and MonitorFromRect. The screen's device context handle is retrieved via CreateDC using the screen's DeviceName property, enabling direct drawing on specific monitors.

Precise Window Placement on Specific Monitors

Accurate window placement on a chosen monitor with SetWindowPos requires these steps:

1. Virtual Desktop Coordinates: Employ SendInput() to simulate mouse clicks, using a POINT structure to define the target position before calling SetWindowPos. This positions the window within the virtual desktop's coordinate system.

2. Monitor-Relative Coordinates: For monitor-specific positioning, calculate the window's position relative to the monitor's origin. Use Screen.FromPoint() to get the Screen object representing the target monitor and its Bounds property to determine the relative position.

DPI Awareness: A Crucial Factor

Applications lacking DPI awareness may experience inaccurate screen positioning due to virtualization and DPI scaling. Ensure DPI awareness by including the necessary entries in your application's manifest file.

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