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I remember seeing the following a lot when I was younger, and recently saw it again in a DOSbox setting:

A gray Windows 3.x desktop, on top of which a single window without a title bar is displayed. Inside the window, there is a maze of red squiggles, and below it there is a progress bar that reads ‘1%’ and the following caption typeset in the System font: Your program is testing for optimal display performance so that it will look its best on your system. This will take a few minutes, but you will only see it again if you change to new display settings. A Program Manager icon is seen below.

For those that haven't seen it, the squiggly red lines shift and undulate quite a bit, and actually looks like it's doing something fairly complicated. What is the program actually doing here? I don't actually know anything about graphics processing, so I assuming that it's performing some kind of stress test on the system, but I have no clue as to what it might be doing behind the scenes. And: If the software is trying to tune itself, how would it know what to change, especially on an older system?

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    Just for context, that’s WinG’s calibration test. – Stephen Kitt Jun 22 '18 at 14:25
  • Huh, just looked it up. Pretty interesting: en.wikipedia.org/wiki/WinG – LSM07 Jun 22 '18 at 14:27
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    I hope it doesn't step on anybody's toes, but I transcribed the in-question answer to a community wiki (i.e. no points allocated) formal answer. That'll ensure this question shows up properly in the various StackOverflow places as not being unanswered. – Tommy Jun 22 '18 at 15:04
  • Yeah, @LSM07, you should post answers as answers in future. We're not like a typical forum. (Obligatory tour link.) – wizzwizz4 Jun 22 '18 at 15:36
  • Thanks @Tommy, I rolled the question back to its first version to avoid having the answer in both places. I do remember reading about the various calls that were compared, if I find it again I’ll add the information... – Stephen Kitt Jun 22 '18 at 15:37
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Well, turns out the Wikipedia article has the answer already:

WinG would also perform a graphics hardware/driver profiling test on the first execution of the program in order to determine the best way to manipulate the graphics hardware. This test showed a window full of red curved lines, sections of which would wobble as performance was tested. Once WinG had determined the fastest calls that did not cause graphics corruption, a profile would be saved so that the test would not need to be performed again.

Thanks to Stephen Kitt for the comment of what to look up, "WinG"

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    What operations would cause graphics corruption? What did he contents of a profile like look like? – Dai Mar 21 '20 at 19:50
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    @Dai: There were a number of ways of writing to the display, either directly or through the use of acceleration hardware. Part of the purpose of acceleration hardware was to allow the CPU to request that the display card do something, and then have the CPU move on to other tasks while the display card processes the action autonomously. On some cards, if the CPU asked the display card to perform a write to an area of the screen and the CPU then immediately wrote to that area before the display card completed the action, the data written by the CPU would get overwritten when the card... – supercat Feb 18 at 16:02
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    ...got around to processing the requested action. On other cards, any request to write the display directly would stall until all pending accelerator actions had completed. Some drivers might keep a list of "dirty rectangles" for which operations had been requested but not completed, and stall any attempts to write data within those rectangles but allow others to proceed without impediment. – supercat Feb 18 at 16:04
  • @supercat Yes, but that doesn't explain the necessity for WinG's graphics testing window - or how different operations would cause graphics to wobble. – Dai Feb 18 at 16:32
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    @Dai: The testing program would do things ask the graphics controller to copy a shape from one part of the screen to another, and then immediately directly draw to the destination area of the screen, and then test whether the operation succeeded and how long it took. I'm not sure why the pipe shapes in particular were chosen. – supercat Feb 18 at 16:37

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