RFR: 8282270: java/awt/Robot Screen Capture tests fail after 8280861 [v2]

[Maxim Kartashev]

On Mon, 28 Feb 2022 14:54:19 GMT, Maxim Kartashev <duke at openjdk.java.net> wrote:

>> The two tests `ScreenCaptureGtkTest.java` and `HiDPIRobotScreenCaptureTest.java` under `java/awt/Robot/HiDPIScreenCapture` started to intermittently fail under Windows and Linux after the [recent changes](https://github.com/openjdk/jdk/commit/cc7cf81256ed4d74493472017b1c4df20fa2208a) made exclusively for the Linux `Robot` implementation.
>> 
>> `HiDPIRobotScreenCaptureTest.java`
>> Since the Windows failures cannot possibly have their origin in the fix made - the latter being Linux-only - the test apparently either exposes an existing bug in the Windows `Robot` or is bumping against a peculiarity of that platform. The test is reverted back to its original form that didn't fail.
>> 
>> `ScreenCaptureGtkTest.java`
>> The coordinates in the log `(83, 78)` of a failure are higher up than the test suggests `(83, 97)`. I've seen similar failures on Ubuntu 20.04 when the coordinates were set to `(0, 0)`. The color then picked matched the color of the bar drawn at the top of the screen. I believe it's best to place the test pixels towards the center of the window to avoid desktop elements interference.
>> 
>> The other possible reason for intermittent failures are window coordinates. Suppose that the test is executing with `sun.java2d.uiScale` set to 2. This effectively means that it can only pick colors of pixels at even coordinates (in the absolute desktop space). So if the window is placed at, say, `(201, 201)`, `Robot` can only pick the color at either `(200, 200)` or `(202, 202)`. Since the test only makes sense if it is pixel-accurate, I removed all `@run`s with `sun.java2d.uiScale` other than 1. This way window placement will not cause a failure.
>> 
>> This was tested on Ubuntu 20.04 and 18.04 with desktop scaling set to 100%, 200%, and 300%.
>
> Maxim Kartashev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixed HiDPIRobotScreenCaptureTest to save image on failure

Updated the failing test by increasing the delay between when the frame is shown and image capture. Also, added code to save an image in case of failure. The change was verified on Ubuntu 20.04 and Windows 10.

@aivanov-jdk  Could you please re-run the test? Thanks once more!

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PR: https://git.openjdk.java.net/jdk/pull/7613