On Tue, 19 Jan 2021 00:57:31 GMT, Sergey Bylokhov <s...@openjdk.org> wrote:
> We use two different approaches to listing the display modes on the system: > - For single-screen configuration use version 1.1 protocol > XRRGetScreenInfo/XRRConfigRates/XRRConfigSizes > - For multi-screen configuration use version 1.2 protocol: > XRRGetScreenResources/XRRGetOutputInfo/XRRModeInfo > > Unfortunately, the current code does not work for some specific double scan > modes, it doubles the real refresh rate. If this refresh rate will be passed > to the Xserver later it could hang/crash. > > The same bug existed in xrandr utility before version 1.4: > https://bugs.freedesktop.org/show_bug.cgi?id=37043 > https://gitlab.freedesktop.org/xorg/app/xrandr/commit/7fd4f18b649f22fad4dbf9fc64b69b3e7f172207 > > As suggested in the bug report I have tried to unify the code for single and > multiscreen systems and use updated code currently used on the multiscreen. > > But unfortunately, I have found that the multi-screen code is even more > broken. The problematic code is this: > > int scr = 0, out = 0; > if (usingXinerama && XScreenCount(awt_display) > 0) { > out = screen; > } else { > scr = screen; > } > The idea of the code is: if the passed screen is Xinerama index used by the > java2d, then the "scr" will be zero, and "out" will be the "virtual" index > for that screen. If the screen is X11 screen then "src" will be the correct > screen and "out" will be zero. > > The problem is that the code assumes that xrandr expect the "virtual" index > as the "out" parameter, but this is not. This parameter is the index of the > "output" such as DP1, DP2, other ports/etc. > > So sometimes the code works when the first screen is connected to the first > port on the video card and the second screen to the second port, otherwise, > we just report data for the wrong screen or report nothing. > > I did not found a reliable way to map Xinerama srceens to the xrandr. It is > better to rework the java2d to use the xrandr instead of xinerama. > > As a fix, I suggest dropping the code which uses the incorrect mapping > screen->output. This includes the code related to the display modes added in > the JDK-8167486 + JDK-8022810, and also the code related to the calculation > of scale factor from the "ubuntu property" which does not work on the recent > ubuntu version after migration to gnome3 added in the JDK-8149115 > > I will file a separate two bugs to reimplement this functionality, most > probably the "display modes" will be implementing when we fully migrate to > the xrandr, and calculation of the scale factor will be implemented via the > gtk library. I guess not having this functionality at all is better than having a code that hangs. Can we have these new bugs about re-implementing this functionality linked in the initial bug so they can be tracked easier? ------------- Marked as reviewed by kizune (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/2136
