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

[Erik Joelsson]

On Thu, 4 May 2023 14:18:44 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 a screen capture for all screens or some of them. For screens without permission there will be a black image.
> + If the user wishes to change their mind about the screens allowed to be captured, the user should use the new `Robot#resetScreenCapturePermission` method
> 
> Also added several system properties:
> `awt.robot.screencastEnabled` false by default, uses the ScreenCast API if true
> `awt.robot.screencastDebug` false by default, prints some debug information if true
> 
> For convenience, this change is divided into two commits:
> 1. added [pipewire headers](https://gitlab.freedesktop.org/pipewire/pipewire/) that are needed for the build
> 2. main changes 
> 
> Changes in the documentation are in a separate draft PR (#13809) also for convenience.
> 
> At the moment, the planned supported systems are Ubuntu 22.04+, the latest Oracle Linux 9.1 and RHEL 9.1 has some issues with restore_token support.

I would like to understand why we need to add third party headers to our source tree. Are these not generally available on Linux systems?

You say that the functionality isn't enabled by default, is that a runtime thing? It loos like it will be built unconditionally.

make/modules/java.desktop/lib/Awt2dLibraries.gmk line 194:

> 192:     LIBAWT_XAWT_EXCLUDES := medialib debug
> 193: 
> 194:     BUILD_LIBPIPEWIRE_HEADER_DIRS := \

This variable name indicates that LIBPIPEWIRE is a library that we would build, but it seems to just be headers. I would suggest dropping the `BUILD_` prefix.

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

PR Review: https://git.openjdk.org/jdk/pull/13803#pullrequestreview-1413812683
PR Review Comment: https://git.openjdk.org/jdk/pull/13803#discussion_r1185452739