The bug doesn't reproduce anymore. Both the extracted-from-xfwm4.c test program and xfwm4 now work, on my Ubuntu 16.04 machine with the NVIDIA GeForce 750 Ti card. I configured it back to nouveau and enabled compositing.
I'm guessing an update fixed it? $ lsb_release -rd Description: Ubuntu 16.04.2 LTS Release: 16.04 $ uname -a Linux atom 4.4.0-77-generic #98-Ubuntu SMP Wed Apr 26 08:34:02 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux $ apt-cache policy xorg xorg: Installed: 1:7.7+13ubuntu3 Candidate: 1:7.7+13ubuntu3 Version table: *** 1:7.7+13ubuntu3 500 500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages 100 /var/lib/dpkg/status $ apt-cache policy xserver-xorg-video-nouveau xserver-xorg-video-nouveau: Installed: 1:1.0.12-1build2 Candidate: 1:1.0.12-1build2 Version table: *** 1:1.0.12-1build2 500 500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages 100 /var/lib/dpkg/status (I suppose I should have included libcairo2 originally?) $ apt-cache policy libcairo2 libcairo2: Installed: 1.14.6-1 Candidate: 1.14.6-1 Version table: *** 1.14.6-1 500 500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages 100 /var/lib/dpkg/status (The xfmw4 version number is bogus -- I'm using my own patched version to work around an incompatibility with VirtualBox.) $ apt-cache policy xfwm4 xfwm4: Installed: 4.12.3-9ubuntu2 Candidate: 4.12.3-9ubuntu2 Version table: *** 4.12.3-9ubuntu2 100 100 /var/lib/dpkg/status 4.12.3-1ubuntu2 500 500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1606122 Title: Cairo drawing coordinates are broken w/nouveau (affects xfwm4) Status in xorg package in Ubuntu: New Bug description: I'm using xfwm4 with Xubuntu 16.04. With compositing enabled, and when I cycle through windows with Alt-Tab, xfwm4 draws an opaque rectangle bordering a candidate window, and it fills that rectangle with a semi-transparent blue color. When I use the nouveau driver, the filled rectangle is clipped. The problem does not reproduce with the proprietary nvidia driver. It seems as though a drawing command should be issued using a window- relative coordinate, but sometimes is instead issued using a screen- relative coordinate. I extracted relevant bits of xfwm4 into a small test program that reproduces the problem. The test program creates a transparent XWindow at (100,100) with size (210,210). It draws six rectangles centered inside the window of varying parameters. Two of them are drawn at the wrong place. xfwm4 should be off-the-hook, I think, unless it's doing something wrong (e.g. unspecified/undefined behavior). $ lsb_release -rd Description: Ubuntu 16.04.1 LTS Release: 16.04 $ apt-cache policy xserver-xorg-video-nouveau xserver-xorg-video-nouveau: Installed: 1:1.0.12-1build2 Candidate: 1:1.0.12-1build2 Version table: *** 1:1.0.12-1build2 500 500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages 100 /var/lib/dpkg/status $ apt-cache policy xfwm4 xfwm4: Installed: 4.12.3-1ubuntu2 Candidate: 4.12.3-1ubuntu2 Version table: *** 4.12.3-1ubuntu2 500 500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages 100 /var/lib/dpkg/status I created a video demonstrating the problem in xfwm4: https://www.youtube.com/watch?v=8dZN80tMA6M. If you look closely, you can see that the opaque blue border is positioned correctly, while the semi-transparent overlay isn't. FWIW, I'm using an NVIDIA GeForce GTX 750 Ti card. ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: xorg 1:7.7+13ubuntu3 ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13 Uname: Linux 4.4.0-31-generic x86_64 ApportVersion: 2.20.1-0ubuntu2.1 Architecture: amd64 CurrentDesktop: XFCE Date: Mon Jul 25 00:50:21 2016 InstallationDate: Installed on 2016-07-19 (6 days ago) InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1) SourcePackage: xorg Symptom: display UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1606122/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp