Using iPad as a Secondary Display
Having multiple displays on a computer is a huge productivity boost for me. With two displays connected both to my dock both in the office and at home, most of my needs are covered. But for a long time, the built-in display on my laptop had to be enough while traveling. At least until I saw a friend of mine using his iPad as the second display.
He told me about Duet Display and I started using it regularly. I always travel with my iPad anyway so I don't even have to bring any extra hardware with me. Whenever I have room for it, I simply connect the iPad to my laptop and have additional screen real estate at my disposal. I even use it when giving talks if I have a lot of demos. It's great for notes and code snippets.
However, having Duet installed broke 3D accelerated graphics on my computer. Most of games stopped working: they only showed a black screen or even crashed. Since I'm not gaming regularly on my laptop I didn't even notice it immediately. This made it more difficult to troubleshoot the issue. The only thing I had to work with, was the error that some games displayed:
Failed to initialize Direct3D. Make sure you have at least DirectX 9.0c installed, have drivers for your graphics card and have not disabled 3D acceleration in display settings. InitializeEngineGraphics failed
I tried running DxDiag first but it didn't find any errors. The display driver was also up-to-date. I started suspecting the latest Windows 10 update I installed recently but I quickly dismissed it because I couldn't find any mention of others having similar issues.
I identified Duet Display as the cause only after I started systematically reviewing and uninstalling software I installed recently. As soon as I uninstalled it, the problem was gone. And I wasn't the only one having these issues either. Reading forum posts about it, I found an alternative: Splashtop Wired XDisplay. So far, it seems to work just as good, but most importantly - it doesn't break Direct3D on my machine if I have it installed.