ros-kinetic/opencv3 doesn't build with >=sci-libs/vtk-8.2.0

[awesomebytes]

Just a warning for anyone else that may run into it.

ros-kinetic/opencv3 is a snapshot of a tarball (with disabled tests and examples as explained here) which is a bit of a pain to recreate.

The errors look like this:

2020-05-18T06:25:45.1708233Z /tmp/gentoo/var/tmp/portage/ros-kinetic/opencv3-3.3.1-r5/work/opencv3-3.3.1/modules/viz/src/clouds.cpp: In constructor 'cv::viz::WCloud::WCloud(cv::InputArray, cv::InputArray, cv::InputArray)':
2020-05-18T06:25:45.1709811Z /tmp/gentoo/var/tmp/portage/ros-kinetic/opencv3-3.3.1-r5/work/opencv3-3.3.1/modules/viz/src/clouds.cpp:80:13: error: 'class vtkPolyDataMapper' has no member named 'ImmediateModeRenderingOff'
2020-05-18T06:25:45.1710700Z    80 |     mapper->ImmediateModeRenderingOff();

The workaround is, meanwhile 8.1 lasts in the gentoo tree, to mask >8.2. If it lasts a year, it will last until the EOL of Kinetic anyways. Alternatively, if it comes to it, we can add to ros-overlay in sci-libs the last 8.1 ebuild.

[awesomebytes]

Also, not directly related to that, but vtk-8.2.0 right now doesn't build correctly as it needs media-libs/glew and dev-libs/plugixml and they aren't declared in their dependencies, they must be emerged by hand first. As reported here for glew and here for plugixml