splashscreen protocol

[alexey.ushakov at jetbrains.com]

Hello Phil et al.,

Here is pure wayland implementation of splash screen that we created
within WLToolkit. It supports splash image and Graphics rendering
capabilities so, it maybe useful to see what api is actually needed
from wayland side.

https://github.com/openjdk/wakefield/blob/jdk21.0.1-wayland/src/java.desktop/unix/native/libwlsplashscreen/splashscreen_sys.c

Best Regards,
Alexey   

On Thu, 2024-05-23 at 13:42 -0700, Philip Race wrote:
> w.r.t the discussion we had about the Wayland splash screen protocol 
> proposal and whether it might work for JDK/AWT
> splash screen's need for centering a window.
> 
> - Usage of splash screen looks like "java -splash:myimage.png
> MyJavaApp"
> - That image is displayed in a "native" window (ie not an AWT one)
> and 
> that is a "raw" XWindow on Linux today
> and I suppose would be  something like an XDG toplevel with wayland.
> - That 'native' splash window is shown before the VM is running (ie 
> before any classes are loaded / Java code is running)
> -  It is the same native window that is indirectly exposed in the AWT
> SplashScreen API
> https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/java/awt/SplashScreen.html
> - Note that apps CANNOT get a direct reference to the window, so they
> are entirely limited by the SplashScreen API
> - Applications can composite rendering on to that window by getting a
> "Graphics" instance and draw to that and
>     then make a call update() the splash contents
> - The window is definitely "output only", so I think that part fits
> into 
> the proposed protocol.
> - The fairly limited rendering you can do means that applications
> which 
> want to do more, typically put up a new AWT window
>   in the same exact location and with the same size.
> - SplashScreen does have a "getBounds()" API which returns the x/y
> and 
> w/h of the window.
> - Applications can then use that to create their window, which when 
> displayed automatically causes the splash window
>     to be hidden.
> 
> I think in the context of the usual Wayland policies that "getBounds"
> might be the tricky part. The X/Y part that is.
> Although in many cases we could probably calculate it IIUC 
> xdg_output.logical_size will give us
> overall bounds of a device and if we know the w/h of our window -
> then 
> it should be
> simple arithmetic to calculate the X/Y .. and assuming most Wayland
> apps 
> know how big a splash window they created
> they can do the same .. and so perhaps there's no reason for the
> splash 
> screen protocol to try to "hide" this information.
> 
> In summary, a simple splash screen protocol that supports centering 
> would probably work for JDK/AWT.
> 
> -phil.
> 
> 
> 
>