Spent some time over the weekend looking at APIs in windows that give access to the monitor configuration of the system that code is running on.

I tend to run on systems with several monitors (usually as many as is practical). Ideally, I’d like to create tools that can use the available display real-estate in helpful ways.

The main API involved is EnumDisplayMonitors which will invoke your provided callback function with the HMONITOR for each monitor that is recognized by the system. Calling GetMonitorInfoW can then provide some of the details of each display in a MONITORINFOEX structure.

One oddity in all of this is that a monitor with a scaling factor applied (my 4K monitor is set to 150% scale factor for usability reasons) returns the post-scaling size with a gap in the coordinate system that reflects the ‘missing’ pixels. In my case the small monitor I use to keep an eye on the router is logically far to the right of the left hand edge of the big monitor.

There is a supplementary API call GetScaleFactorForMonitor which returns a DEVICE_SCALE_FACTOR indicating the current scale factor for a given monitor. This is a little bit strange on my system as the big monitor appears to be set for 150% scaling but the API call shows 140% scaling. The size numbers match what I’d expect for 150% so something must be a bit off here…

Interesting API to look into GetDpiForMonitor and MONITOR_DPI_TYPE.

Looks as if the SetProcessDpiAwareness API (with PROCESS_DPI_AWARENESS and WM_DPICHANGED) may have a part in all of this as well…deciding whether the process gets presented DPI aware or virtualized display metrics.

Curious translation in GetPhysicalMonitorsFromHMONITOR  could use a bit of a look.

I need to read more of the DPI aware and multi-monitor articles before I’m done here. I also want a better idea of how this functionality interacts with WPF user interfaces as I’m likely to build the upper layers that way.

This certainly gets more complicated with display scaling and DPI calculations in the mix.

Some more relevant articles (I haven’t read these all in detail yet):

• High DPI Desktop Application Development on Windows
• Improving the high-DPI experience in GDI based Desktop Apps
• Coding for High-DPI Displays in Windows
• Developing a Per-Monitor DPI-Aware WPF Application
• High DPI Scaling Improvements for Desktop Applications and “Mixed Mode” DPI Scaling in the Windows 10 Anniversary Update (1607)
• Understanding Screen Scaling Issues
• Multiple Display Monitors