Update needed dependencies

Fixes #2683

CHANGELOG.asciidoc

@@ -17,6 +17,15 @@ This project adheres to http://semver.org/[Semantic Versioning].
 v0.11.0 (unreleased)
 --------------------
 
+New dependencies
+~~~~~~~~~~~~~~~~
+
+- New dependency on `PyQt5.QtOpenGL` if QtWebEngine is used. QtWebEngine depends
+  on QtOpenGL already, but on distributions packaging split PyQt5 wrappers, the
+  wrappers for QtOpenGL are now required.
+- New optional (but recommended) `PyOpenGL` dependency with QtWebEngine to work
+  around a bug where a black screen is shown with some setups.
+
 Added
 ~~~~~
 
@@ -87,7 +96,7 @@ Fixed
 - (QtWebEngine) Added a workaround for a black screen with some setups
   (the workaround requires PyOpenGL to be installed, but it's optional)
 - (QtWebEngine) Starting with Nouveau graphics now shows an error message
-  instead of crashing in Qt.
+  instead of crashing in Qt. This adds a new dependency on `PyQt5.QtOpenGL`.
 - (QtWebEngine) Retrying downloads now shows an error instead of crashing.
 - (QtWebEngine) Cloning a view-source tab now doesn't crash anymore.
 - (QtWebKit) The HTTP cache is disabled on Qt 5.7.1 and 5.8 now as it leads to

INSTALL.asciidoc

@@ -185,8 +185,9 @@ with:
 # xbps-install qutebrowser
 ----
 
-It's currently recommended to install `python-PyQt5-webengine` and start with
-`--backend webengine` to use the new backend.
+It's currently recommended to install `python3-PyQt5-webengine` and
+`python3-PyQt5-opengl`, then start with `--backend webengine` to use the new
+backend.
 
 On NixOS
 --------

README.asciidoc

@@ -98,11 +98,11 @@ Requirements
 
 The following software and libraries are required to run qutebrowser:
 
-* http://www.python.org/[Python] 3.4 or newer
-* http://qt.io/[Qt] 5.2.0 or newer (5.5.1 recommended)
+* http://www.python.org/[Python] 3.4 or newer (3.5 recommended)
+* http://qt.io/[Qt] 5.2.0 or newer (5.9.0 recommended)
 * QtWebKit (old or link:https://github.com/annulen/webkit/wiki[reloaded]/NG) or QtWebEngine
 * http://www.riverbankcomputing.com/software/pyqt/intro[PyQt] 5.2.0 or newer
-(5.5.1 recommended) for Python 3
+(5.8.1 recommended) for Python 3
 * https://pypi.python.org/pypi/setuptools/[pkg_resources/setuptools]
 * http://fdik.org/pyPEG/[pyPEG2]
 * http://jinja.pocoo.org/[jinja2]

qutebrowser/misc/earlyinit.py

@@ -314,6 +314,7 @@ def check_libraries(backend):
     if backend == 'webengine':
         modules['PyQt5.QtWebEngineWidgets'] = _missing_str("QtWebEngine",
                                                            webengine=True)
+        modules['PyQt5.QtOpenGL'] = _missing_str("PyQt5.QtOpenGL")
     else:
         assert backend == 'webkit'
         modules['PyQt5.QtWebKit'] = _missing_str("PyQt5.QtWebKit")