RFR: 8354415: [Ubuntu25.04] api/java_awt/GraphicsDevice/indexTGF.html#SetDisplayMode - setDisplayMode_REFRESH_RATE_UNKNOWN fails: Height is different on vnc

[Alexander Zvegintsev]

On Fri, 11 Jul 2025 15:47:33 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

> On Linux, we are currently use XRRSetScreenConfigAndRate to change the display mode. This works in most cases, except for some VNC-configured hosts, where the display change may not occur.
> One of the conformance tests fails on these hosts.
> 
> It was discovered, that the xrandr utility app works fine on these hosts and uses the Crtc and Output Randr APIs, which provide more fine-grained control over display settings.
> 
> This changeset utilizes the Crtc and Output Randr APIs to change the display mode.
> 
> Currently, changing the display mode is only [available when running a single screen](https://github.com/openjdk/jdk/blob/a86dd56de34f730b42593236f17118ef5ce4985a/src/java.desktop/unix/classes/sun/awt/X11GraphicsDevice.java#L365).
> This limitation remains, but we may remove it in the future. A separate issue [has been filed](https://bugs.openjdk.org/browse/JDK-8361968) for this purpose.
> 
> The `awt.x11useOldConfigDisplayMode` system property enables the old behavior. Perhaps there's a better name for it.
> 
> Testing looks good on VNC and local machines.

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PR Review: https://git.openjdk.org/jdk/pull/26268#pullrequestreview-3018818082