RFR: 8280982: [Wayland] [XWayland] java.awt.Robot taking screenshots [v9]

[Phil Race]

On Wed, 31 May 2023 15:03:04 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

>> Modern Linux systems often come with [Wayland](https://wayland.freedesktop.org/) by default.
>> This comes with some difficulties, and one of them is the inability to get screenshots from the system.
>> This is because we now use the [X Window System API](https://en.wikipedia.org/wiki/X_Window_System) to capture screenshots and it cannot access data outside the [XWayland server](https://wayland.freedesktop.org/xserver.html) 
>> 
>> But this functionality is a very important part of automated testing.
>> 
>> 
>> At the moment there are two obvious solutions to this problem, and both use [xdg-desktop-portal](https://github.com/flatpak/xdg-desktop-portal):
>> 
>> 1. [org.freedesktop.portal.Screenshot DBUS API](https://flatpak.github.io/xdg-desktop-portal/#gdbus-org.freedesktop.portal.Screenshot)
>> It has several drawbacks though:
>> + It saves a screenshot to disk, which must be read and deleted(may add some delays depending on the type of a disk drive).
>> + There is no way to disable the visual "screen flash" after screenshot
>> + It asks a user confirmation to save a screenshot. This confirmation can be saved on Gnome 43+. 
>> Since we would like Ubuntu 22.04 LTS which comes with Gnome 42 this option is not acceptable for us because it would require user confirmation for each screenshot.
>> But we still can consider this option as a fallback.
>> 
>> 
>> 
>> 2. [org.freedesktop.portal.ScreenCast](https://flatpak.github.io/xdg-desktop-portal/#gdbus-org.freedesktop.portal.ScreenCast)
>> It typically used by applications that need to capture the contents of the user's screen or a specific window for the purpose of sharing, recording, or streaming.
>> This might be a bit of overkill, but it avoids several of the problems mentioned in the Screenshot API.
>> 
>> + implementation is more complicated comparing to Screenshot API
>> + no intermediate file, screenshot data can be obtained from memory
>> + Permission to make screenshots can be stored with [`restore_token`](https://flatpak.github.io/xdg-desktop-portal/#gdbus-method-org-freedesktop-portal-ScreenCast.SelectSources)
>> 
>> 
>> So this PR adds the ability to take screenshots using the ScreenCast API. This functionality is currently disabled by default.
>> 
>> This change also introduces some new behavior for the robot:
>> A system window now appears asking for confirmation from the user to capture the screen.
>> + The user can refuse the screen capture completely. In this case a security exception will be thrown.
>> + The user can allow...
>
> Alexander Zvegintsev has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - improve retVal processing
>  - address token storage comments
>  - removing non-ascii
>  - EXCEPTION_CHECK_DESCRIBE_CLEAR -> EXCEPTION_CHECK_DESCRIBE

I'm getting pretty consistent testing results now - meaning the ones that have known
issues are the ones that fail, and I've looked at the code sufficiently.
The restore token seems to be behaving properly now.

I did have one case I've not understood where a test system got very confused about the display resolution of the monitor and needed a full power cycle.
I don't know if a specific test caused that or it was something else, but it isn't repeatable (at least not yet) so shouldn't block integration.

I am quite sure that SOME of the test failures are unstable tests that we've been lucky with all these years  and xwayland is now showing up the instability. Things un-related to robot and more about timing for the most part. Although there's one test that seriously over-stresses robot with > 10,000 calls in a loop to getPixelColor() I'll see if I can push test update fixes to at least some of these to reduce noise.

But I'm OK to approve now.

-------------

Marked as reviewed by prr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13803#pullrequestreview-1454093265