Raymond Chen: The cats sitting on a fence in early builds of Windows 8

Here’s a fun post from Microsoft’s Raymond Chen, of The Old New Thing fame:

The Windows 8 tablet experience organized its components as a collection of layers, with each layer stacked on top of the next one. For the purpose of today’s discussion, the important layers are the Start layer and the Apps layer: If you’re using an app, then the Apps layer is full screen. If you have opened Start, then the Start layer covers the Apps layer. If the last app exits, then Start automatically opens. There should be a fullscreen layer at all times.

During development, of course, something inevitably goes wrong, and you get into states where neither the Start nor the Apps layer is being shown, resulting in a black screen.

Now, a black screen could have multiple causes. The video driver may have crashed. Or the video driver could be working fine, but the compositor has crashed, so that nothing is being given to the video driver. Or the compositor could be working fine, but the shell has crashed, so the compositor has nothing to render. Or the shell could be running, but it simply forgot to put something on the screen.

For that last case, the Windows 8 shell created a backstop window that sat at a layer below all of the other layers. If none of the other layers were present, then at least you got a backstop window. And in early debug builds, that backstop window contained an ASCII drawing of cats. That way, if you saw cats, you knew that you were in that last failure case: The shell is running but forgot to put something on the screen.

Why cats?

I guess the developer who wrote the backstop window liked cats.

In fact, the developer who wrote the backstop window liked cats so much, they had a series of cat pictures. At system startup, they drew the first cat picture onto the backstop window, and each time the backstop window was asked to repaint, they cycled to the next picture. It was like a story that was told one sentence at a time, with each sentence revealed the next time there was a catastrophic failure.

In practice, the full story was never told, since we almost never got past even the first picture.

Until now.

Check out the original post for the full story.