June 2016 | The Old New Thing

2016 mid-year link clearance

Raymond ChenJune 30, 2016Jun 30, 201606/30/16

Here it is again: The semi-annual link clearance. GardenCast is a video podcast that deconstructs Olive Garden commercials Each episode picks a 15-second commercial and watches it over and over and over and over. And over. Episode 1. Other episodes follow. Watch them if you dare. Maternal kisses ...

How can I detect whether the Game Bar is covering my window?

Raymond ChenJune 29, 2016Jun 29, 201606/29/16

Pressing the Win+G hotkey opens the Game Bar, which lets you record game clips and screenshots. Actually, I use it a lot even for programs that aren't games: It's great for taking video clips of a bug. Anyway, maybe you have a program that wants to know when the Game Bar is on screen. For example, if you're a game, you may want to pause the ...

Why does the Windows calculator generate tiny errors when calculating the square root of a perfect square?

Raymond ChenJune 28, 2016Jun 28, 201606/28/16

Try this: Fire up the Windows calculator and ask it to compute √4 − 2. The answer is not zero. It's −1.068281969439142e−19. "I thought the Windows calulator used an arbitrary precision arithmetic library. How come the answer isn't exactly zero?" If you read closely in that article, you'll see that it says that the ...

If I have multiple attached keyboards, how can I read input from each one individually?

Raymond ChenJune 27, 2016Jun 27, 201606/27/16

Raw Input is a feature of Windows that lets you obtain keyboard, mouse, or generic HID input. Okay, the generic HID input is nice, but the thing that is interesting today is the fact that the keyboard and mouse input is tagged with the device that generated it. This means that if you have multiple keyboards connected to your computer (say, the...

Why is my message queue full of WM_TIMER messages?

Raymond ChenJune 24, 2016Jun 24, 201606/24/16

Dmitry wondered how it's possible for a lot of auto-generated messages to pile up in the message queue. I remarked, "That's a good question, and I didn't provide all the information necessary to answer it. Answering it will take more than two sentences, so I will toss it onto the topic queue." One of my colleagues wrote to me and said, "Hey, ...

Why does the x64 calling convention reserve four home spaces for parameters even for functions that take fewer than four parameters?

Raymond ChenJune 23, 2016Jun 23, 201606/23/16

In the comments to Can an x64 function repurpose parameter home space as general scratch space?, many people questioned why the full four home spaces are allocated for all functions, even those that have fewer that four parameters. MSDN gives a very brief answer: "This aids in the simplicity of supporting C unprototyped functions, and vararg ...

Using the Windows::Globalization::Calendar object from a Win32 app

Raymond ChenJune 22, 2016Jun 22, 201606/22/16

The Windows.Globalization.Calendar object is documented as supported for use by both Windows Store apps and desktop apps. The UWP samples repo has a Calendar sample that demonstrates how to use it from a Windows Store app, but how do you use it from a desktop app? That's our motivation for looking at the Windows Runtime ABI. Normally, these ...

How to recognize DNS zone scavenging availability timestamps from quite a long way away

Raymond ChenJune 21, 2016Jun 21, 201606/21/16

A customer couldn't figure out how to decipher the scavenge available value that is produced by the dnscmd /zoneinfo command: (If you want to see what it looks like in French, here ya go.) The customer liaison found an old article of mine on decoding timestamps but none of the tricks on that page worked. So what is the format for the ...

Peeking inside an IShellItem to see what it’s made of

Raymond ChenJune 20, 2016Jun 20, 201606/20/16

Windows XP introduced the IShellItem interface which represents an item in the shell namespace. This encapsulates what traditionally is represented by a pair of things, the the IShellFolder interface and an ITEMID_CHILD. The shell item lets you carry just one object around instead of two. Another way of representing an item in the ...

How can I update my WinForms app to behave better at high DPI, or at normal DPI on very large screens?

Raymond ChenJune 17, 2016Jun 17, 201606/17/16

A customer had a WinForms app that was showing its age. It didn't scale itself properly on high-DPI screens, which means that if you ran it on a Surface Pro 4, you got a teeny-tiny window and then you had to go grab your magnifying glass in order to read it. The customer noted, "When the program is run on a large display, it occupies only a ...

The Old New Thing