RFR: 8274939: Incorrect size of the pixel storage is used by the robot on macOS

[Alexey Ivanov]

On Fri, 8 Oct 2021 10:23:13 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> In JDK 9 the native code for the robot class was reworked to get an access to the HiDPI quality screenshots. So we allocate the data storage for the HiDPI quality and then request the best quality from the macOS.
> 
> It works fine if the user request the screenshot of some area, since we properly scale this area. Unfortunately it does not work well if the user request only one pixel, in this case we allocate the array of one element and does not multiply the size by the scale, so if the system scale is 2 then the macOS returns the 2x2 pixels, which does not fit properly to the array of one element. This can be checked by the Xcheck:jni option which produce fatal error in this case.
> 
> Solution is to allocate the storage of the proper size 1 * scale * 1 * scale

I think increasing the buffer according to the scale is correct as the `scale` × `scale` image where `scale != 1` can't fit into the buffer of size 1.

It may not fix other bugs or test failures; buffer overrun is not a good thing and it's fixed.

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Marked as reviewed by aivanov (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5864