Roman Gilg authored Jan 02, 2020 and David Edmundson committed Feb 28, 2020

Summary:
In case the hardware is not able to rotate the output for the configured
rotation value do this rotation in a post-process step.

For that rendering the current view into a separate framebuffer bound to a
texture that then gets sampled to the default framebuffer in an additional
rendering pass through a simple shader rotating it.

This allows us to leave the Effects system and internal model-view-projection
matrix untouched. The rotation in the post-processing step is isolated.

BUG: 389665
FIXED-IN: 5.18

Test Plan: With KScreen all rotations work.

Reviewers: #kwin

Subscribers: davidedmundson, PureTryOut, z3ntu, zzag, univerz, kwin

Tags: #kwin

Maniphest Tasks: T6106

Differential Revision: https://phabricator.kde.org/D25907