Java swing applications not rendering properly with VNC

TL;DR

• Java and glxgears expect a color depth of 24.
• Make sure that X and VNC are set to use a depth of 24 and not some other depth like 16 or 32.

Details:

I had blank Java windows in VNC too, but with Java 7 and Java 8, so it wasn't much of a surprise that disabling xrender didn't help me. That probably makes it a gross violation of StackOverflow protocol to post this here, but I found my way here, so surely others will too. -Dsun.java2d.opengl=true made the text visible, though the anti-aliasing was like something out of the 1980s with a messed up palette, but then I got spuriously transparent parts of windows, always the same parts, cleanly composited, so not like a driver bug. Noticing that glxgears was also displaying with a neat transparent background, when it's opaque black on other systems, I found a thoughtful and informative bug report against "compton", RGBA windows are always transparent #179. Inspired to look at xdpyinfo, I found my VNC server was offering "visuals" of depth 32 only, ie visuals with 8 bits each of red, green and blue and eight bits of alpha. It seems Java, and glxgears, want an opaque visual, so one of depth 24. My normal :0 X server has that as its default. For the -depth switch, man Xtigervnc says "Default is 24, other possible values are 8, 15, and 16 - anything else is likely to cause strange behaviour by applications", yet Debian's provisional packaging for TigerVNC, specifically in /etc/vnc.conf and /usr/bin/tigervncserver, sets it to a default of 32. -depth 24 and suddenly everything was beautiful again, with translucency only where it was requested. xdpyinfo revealed many "visuals" on offer, including depth 32.

On a Linux system, I've found that using the -Dsun.java2d.xrender=false option solved the issue. I think that xrender is now enabled by default on Java 8.

System Properties for Java 2D can be found here : http://docs.oracle.com/javase/8/docs/technotes/guides/2d/flags.html

On Red Hat Enterprise Linux there were two settings in the /etc/xrdp/xrdp.ini file:

uncommented: serverbpp=24 changed existing item: max_bpp=24