<AWT Dev> RFR: 8267430: GraphicsDevice.setDisplayMode(REFRESH_RATE_UNKNOWN) throws AE: Unable to set display mode!

Alexander Zvegintsev azvegint at openjdk.java.net
Mon Jun 7 11:10:02 UTC 2021

On Sat, 5 Jun 2021 15:07:27 GMT, Phil Race <prr at openjdk.org> wrote:

> There are two issues here, both macOS specific.
> First the original reported one that occurs when running on a shared remote VNC type desktop on macOS.
> Only a single supported display mode is returned and it is also the current mode.
> A program that simply enumerates the reported modes and tries to set them, if it reaches the native layer,
> will fail because macOS reports the same display mode it returned as valid as now being illegal.
> It does not appear to be as simple as a user's permission level since it occurs with an admin user as well
> so it probably is the case that macOS simply does not allow this shared desktop to be changed although
> there's no docs I can find
> Ordinarily we would not have tried this since we test if the requested display mode is the same as the native
> one and skip it, but the provided test used REFRESH_RATE_UNKNOWN which is allowed as meaning match
> any mode that satisfies W,H,BPP. But this caused it to fail the equals test so the code is enhanced to check for that
> Second, when creating a test it was discovered that *at least* on the built-in retina display of a 16" macbook pro,
> the system default contig is never in the list of available modes and can be discovered only by querying the *current* mode
> before any modes are changed. This beheaviour is 100% consistent no matter if the system was just rebooted, has
> an external monitor attached as well, or not, activates the discrete card, or not.
> Since we've had code since at least 2013 that added the default mode I suspect this has been seen before but nowhere
> can I find an explanation.
> It has odd consequences like after you change the display mode, you will no longer see the default display mode reported,
> so the list of available modes is reduced by one.
> But for a typical use case which doesn't re-query or more typically caches the original display mode in order to restore it, it presents a bigger problem that trying to restore will always fail. 
> So the other thing this fix does is detect when we fail to restore the initial mode and try again in a different way.
> Only if that fails do we then throw an exception.

src/java.desktop/macosx/native/libawt_lwawt/awt/CGraphicsDevice.m line 266:

> 264: /*
> 265:  * Class:     sun_awt_CGraphicsDevice
> 266:  * Method:    nativeSetDisplayMode



PR: https://git.openjdk.java.net/jdk/pull/4373

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